Older DnD systems like in the infinity games (2.5) is not very fun in my opinion although the games are brilliant. To little diversity in character builds especially for martial classes.
But I've yet to play a CRPG where character building is as much fun as it was in NwN2. The addition of feats and prestige classes made planning your character builds half of the enjoyment.
The only game that comes even close (that I've played) is PoE2, the addition of multiclassing on the already good PoE system makes it versatile enough to be really interesting.
Distinctive classes, loads of options. That's fun. (To me). I think that's what really made me disappointed in DA:O, it has nowhere near the possibilities of DnD 3.5 nor PoE. TDE? Haven't played it in PnP, but at least in the CRPG's that I've played that utilized it levelling felt nowhere near as rewarding as in DnD. That might have been more about implementation though.
Agreed. 1st and 2nd Edition D&D sucked for diversity - and it's also the reason I think a lot of people prefer other systems.
While PoE2 is a huge step forward for their system, it still pales in comparison to 3.5 - not least of which because it's limited to only two classes, and especially because of how they handle active abilities as tied into the class itself, rather than feats you can pick as other classes.
Of course, there's a difference between 3.5 with only Player's Handbook - and then the ridiculous amount of extra material available.
Even so, the nature of multiclassing and the flexibility of the feat and spell system means you will almost literally never run out of builds.
In PoE 2 - there's a much more finite amount of combinations.
As for the best PnP system - that's really down to what you prefer and what you enjoy about PnP.
For me, the best part of PnP is completely separate from the rule system. It's the ability to play any role - and to share a social power fantasy, or any kind of fantasy, really. The ability to say or act in a way that would be counter to the best interests of yourself or others in real life.
Games have yet to enable that to the same extent, and therefore it's a complicated discussion.
I've tried many, many PnP systems in my time. Probably close to 40 or 50.
But I've only played extensively using a handful of systems, including DnD (the first iteration), AD&D, Gurps, Dangerous Journeys, Shadowrun, Drager og Dæmoner, Rolemaster - and a few others.
So, while my experience with PnP is pretty vast - I can't claim to have intricate knowledge of all of them. Far from it.
But, since we're talking about computer games - there's really only a very limited selection from which we can pick and compare.
Fallout SPECIAL is loosely based around Gurps, and Drakensang (old and new) is based on Dark Eye. There are others out there - but the vast majority of computer games are based on either D&D or something unique that the developers themselves came up with.
Also, we need to decide if we're talking about the system in an overall sense, or if we're talking about specific features - including character building, character progression, loot design, combat or other individual features.
I've played hundreds of CRPGs in my time - and I really, truly, struggle to remember a game with a more satisfying OVERALL "game" rule-system than those based around DnD 3+ edition.