Normally, I like class based systems. But then, I've been playing one for seventeen years, and nothing else. I've said before that the first time I looked at a game book that didn't have a class based system (Shadowrun 4th Edition) I was utterly mystified as to how one would play the game. There were no classes (there were templates of suggested abilities like Street Samurai), and without classes, how do you have a character? It was inconceivable to me that a game had no classes. In fact, as much as I love the concept of Shadowrun's setting (fantasy + cyberpunk), I was so shaken I immediately closed the pdf and stepped away from the computer. Later I fell in love with GURPS.
I used to love classes. I attribute this to Stockholm Syndrome. I've ever only played DnD, perhaps the king of class based systems, if not pen and paper RPGs. Nowadays, I find myself wondering about other systems and styles of game, narrative driven rules light systems like FATE, heavy rules heavy versatility like GURPS, Goldilocks systems in terms of versatility and rules load like Savage Worlds, etc, etc, etc.
My beef with class systems, Pathfinder/3.5 in particular, is a major one and minor one at the same time. The classes. I like the combat and skills and feats and race construction, all the rules basically, except the classes. Specifically the structure of those classes. I'll use my knife fighter Hobgoblin Arak to explain this.
Arak is a knife guy, he has lots of them, and is really good at sticking them into other people and swirling them around on their insides. He is good at close up work and he has the muscle and heartiness to back that up, but he's a Hobgoblin and they're generally smaller than a human and kind of wiry and quick. They're bigger, tougher Goblins that aren't terrified of horses, dogs, fire, and the written word, basically.
Now Arak uses knives because he has quick hands and he thinks that the easiest way to surprise a big bruiser with an axe is to look unarmed and then suddenly be bristling with sharp pointy things that make a nice thunking noise when they end up in sensitive or important areas of a body.
Seems like Arak would do well as a Fighter or Rogue, right? Problem is, I don't need skill points or Rogue talents or trapfinding or uncanny dodge and none of those things fit with Arak's background. The only thing I need from Rogue is the sneak attack. Problem with Fighter is that I don't need all the access to heavy armor (Arak has always found it is better to just not get hit in the first place, rather than to strap on fifty pounds of steel and stumble around a dark alley in it waiting to get hit and have your armor stop the blow), I don't need anything from Fighter but the base attack bonus and combat feats. Luckily, Jason is cool and made a Rogue/Fighter combo feat that enables me to get what I need from both classes without sacrificing anything other than six hit points, a +1 of base attack bonus, and having me take this feat. Now this particular build works out pretty well because of Jason's help and my archetype selections, but it is a simple build so it's not exactly a complex thing with a bunch of fiddly bits that need to mesh together.
If I wanted Arak to be good with knives, surprising his enemy with them, and also able to magically hop around a battlefield to add to his general shifty hard to pin down and hit nature? Now I need 6 levels of Sorcerer or Wizard, or 10 levels of Magus or Bard. Those classes have nothing I need though beyond this one ability. Arak didn't go to Hogwarts, his cousin was a battle wizard and had this spell that he used that could hop around short distances, and Arak wanted to learn it too. He has the brain power for it (dimension door is a 4th level spell, Arak's Intelligence in this exercise is 14). With the class based system, Arak could spend six years trying to learn to pull off this one spell, but it is impossible because he doesn't have six or ten levels in one of those classes. Getting this ability would completely fuck up the other two facets of his combat style, he'd lose hit points he needs to survive melee, feats he needs to be good with knives, base attack bonus to strike well with knives, and sneak attack dice to hit hard with his knives. Magus seems like the best of the bad choices. So what would he get instead of this stuff central to his character? A bunch of spells he doesn't need/want, the ability to use those spells in heavier armor, the ability to strike with those spells through a weapon, and the ability to cast the only spell he wants once per day. Plus, with Jason's rules, he'll have a chance of going insane.
Another example I can use is Lance's character Eran. Eran is a Ranger. He is kind of a hunter explorer type of guy. Rangers have animal companions. Eran has never been RPed in such a way that would indicate to me that he has a strong affinity for animals and frolicking among the woodlands befriending aminals and taking them home and cuddling and petting them and loving them forever. An animal companion is a key feature of a Ranger though, so to not utilize it represents kind of a loss of power on the part of the character, so Eran has a wolf because magic. As far as I know, there aren't any Ranger archetypes that lose the animal companion for something else, though I did let Jason trade in his monkey familiar for a feat or something. I am actually thinking of losing the Ranger class from Hekinoe completely and throwing the 3.5 Edition class Scout from Complete Adventurer into the roster. The Ranger always comes off weird to me. Like a Druid/Fighter that is passable at two-weapon fighting or archery (Pathfinder does add a few other options for combat style) and also dislikes some people. It's kind of all over the place. The Scout is much more competent at representing a hunter scout type character in my opinion.
So this dimension door Arak just doesn't work. I have to sacrifice a lot of what I want to do for small taste of other stuff I want to do and a whole bunch of what I don't want to do. This is not optimal. I am sure I could make Magus Arak work. At the very least I could just shocking grasp the fuck out of everything he tries to knife. But that isn't what I want to do with Arak. I want Arak to be the shifty guy slinking around the edge of the fight until he finds a choice target that he can move up next to (or teleport next to) and plunge a dagger home into. If he does get into straight up melee, I want him to use deft knife work to throw his opponent off his game to make his hits more optimal (i.e. feint + sneak attack).
An additional problem are the connotations of taking Rogue levels and what the Rogue class implies. Oh, he's a Rogue, he's a skill guy. No. Arak is not a skill guy. He won't be unlocking doors or finding traps and disarming them. He has no experience with that stuff and will have no ranks in disable device and perception will only have a few because being able to notice your surroundings is smart. Because he's a Fighter there is a certain expectation that he'll be a front line combatant. Arak can do that, but it is not his style. He has no desire to go toe to toe with Johnny the Orc Barbarian and his axe Lucille. He will in fact spend his first round circling away from and around Johnny so he can come at him from behind or the side. Axes hurt and Arak wants to avoid them. Someone else can draw the attention of the axe while Arak works on stopping the brain that moves the muscles behind the axe.
There is a certain expectation of what a character of a certain class can and will do as part of a party. This is easily solved by explaining your character concept to fellow players and GMs, but still there is the expectation. I think we ran into it one time when we expected Karrak to unlock something because he is a Rogue.
Point of post: Classes are restrictive and make it hard for you to tailor a character to what you want to do with them and instead forces you (most of the time) to do what the game designers expect you to do with them. This is usually fine because you expect this going into DnD, Rogues do one thing and Fighters do another and you kind of build your character along those assumptions and it isn't a big deal unless someone decides to make it into one. But once you've seen the cool stuff you can do with a versatile system like GURPS, it can make it hard to reign in the creativity at times.
As a side note, Arak in GURPS would look something like Warp (with limitations like short range, magic, and costs fatigue), Unusual Background to justify the Warp ability, DX+2 - +4 in small blades, and a technique that buys off some of the heavy penalties to skill level for targeting vital areas of the body. Arak built that way would almost definitely come in at under 200 character points.