I like both methods, but only at their extremes.
I like that in Diablo II you had to select class-specific skills. You could play the game 7 times and they would show you 7 completely different aspects of the game.
I like that in Castle of the Winds and Dungeon Seige you had no classes, just attributes that specialised your character. You could create your own classes by training particular skills. It was still possible to play any extreme (warrior, mage, etc.). The problem in this (as I have in Divine Divinity) is that some skills are too useful to ignore (such as Identify) and trying to discipline yourself not to use them can be difficult.
I agree that any one class should be able to complete the game. If you do have classes, then some sections of the game should become totally inaccessable to the other classes. Only a warrior can join the Warrior's Guild, a thief the Thieves Guild, a wizard the Wizard's Guild, and a healer, the Healer's Guild. Each Guild provides equal bonuses for attending them and completing their quests. Also, a warrior may become a part-time body guard, a thief can rob houses at night, a wizard can assist in a greater cause, and a healer could gather rare herbs for a mysterious plague. Only these classes gain access to these quests, all providing equal bonuses.
Can you imagine the replay value in that?
Yes, the replay value would be very high and, IMHO, the player's expirience would be much more meaningful. You would be a
MAGE. Not some guy in pajamas that thinks daggers are too weak so he uses a claymore and meteorstrike for backup but because he's technically a thief he can also sneak.
And yes, if you pick an extreme, the player should both be limited but also greatly rewarded. Have some parts of the game totally inacessable, but also reward the purist for his or her discipline in sticking to one archetype. Remember how in diablo ii every class had like a level 30 skill that was their "Killer Ap'"? Do the same here.
Have just a few skills that are only available later on to the purist. A pure warrior who has a walking lawnmower ability. A mage that has a "Wail of the Banshee mass instant death" type of spell. A thief...well, I can't think of one for the thief. I don't think thieves belong in single character CRPGs (see my post in the suggestions forum "Two suggestions for a very promising series"), but anyway you get my point.
And to expand on another point you made - some skills are way to good for any class to pass up. I never had much use for Identify. I keep most of my loot that I'm not using un-ID anyway. And when I want something ID'd I just pay the 100 gold.
But I'll say right now that if Aura of Protection didn't exist, I would have never made it this far. Early on I had to skimp on my vitality just to be able to equip better equipment. Aura of protection allowed me to do this without being killed every 2 seconds. It was only in my 20's that I began to put more points in vitality. Now with life drain, frost, and heavy armor, Aura of Protection isn't that big of a deal. But early on I will say that I felt that like I had no choice but to use it - much to my annoyance. I could say the exact thing about having to do alchemy to make restoration potions. It was pretty much mandatory early on. And, you guessed it <img src="/ubbthreads/images/graemlins/eek.gif" alt="" />, I don't I should have felt that ANY non warrior skills were mandatory.
