"Lis I have a problem with my players." My brother mentions on the phone while talking with me to fill the silence between my work and my apartment. "They're all Munchkins*." I roll my eyes a little at this only a little jealous that my younger brother has been running a campaign in Dungeons and Dragons and I have yet to run something in anything. But he did have an older sister to guide him into geekdom.
"Well that's what you get when you play 3.5." I put in my normal jibe at his choice of game. To which he replies, exasperated "that's what they said."
It should be noted I don't play a lot of Dungeons and Dragons 3.5 or D20 system (both copyright Wizards of The Coast.) I have played one extensive D20 Star Wars campaign and I once, long ago, played one 3.5 campaign that I dropped out of. My overall impression of the system is blandness. Not that they don't have good points. The GM's and groups I was playing with were fun. The Star Wars game was where the weird intergame intragroup trope of me playing small fuzzy things came from. Yet overall I just don't have a lot of love for the system.
Some good aspects of 3.5: its adaptability. There are many D20 system books out there for almost anything you are a fan of and they can be effectively combined. Want to play a game where a Stargate team goes to a planet where Darth Vader is currently pitching a battle against Cthulu? All you need is those three D20 books (all of which exist). If you are looking for more firm rules in your role playing experience D20 gives you what you need.
Mostly I play Advanced Dungeons and Dragons 2nd ed. There is the fact that this is what the people around me run (or run slight alterations of). I still have to agree with my friends' reasoning for running this system. One of the first is you can make choices as you go. Now I know there are 3.5 players who will say that you can definitely change your mind about a character as it evolves but so many skills have such weird prerequisites that you need to plan everything perfectly in advance half the time. With 2nd ed there are no feats to get prerequisite feats in. The skill system is very simple.
Another problem with D20 is topending. In 2nd ed most rolling for skills is dependent on rolling under your stat. So the higher your skill the more likely you are to roll under it. In D20 all skills have a skill check that you have to get by adding your skill to a d20 die roll. There are examples of why this doesn't work too well. The first example is that it is very easy to just make an unpassable check. A DM can simply set a check so high that a player can't possibly make it. The other end of the scale I like to use a personal story to tell people about. In the starwars game I played I was a tech specialist. All of my skills were maxed to mechanic repair, astrogating, piloting and computer use. At one point we were doing something that involved breaking into a computerized lock. I made a roll of like a 4 and had enough skill points that when I said what my final roll was (I honestly can't remember it was somewhere in the 30s I think) the GM just said there was basically no way I could fail this roll as the challenge ratings were all below my skill numbers. I couldn't shoot worth a damn (all combat skills were hard to get with my class I wasn't trying to minmax but it just happens) in combat my best bet was hiding which I sucked at. But if we had to fly somewhere or hack something there wasn't even a brief moment of "oh maybe she won't make this" tension. I just automatically did it, rolling was a pointless action that I took to make it feel like I as a player had some contribution.
The third and final problem I have with D20 is it is hard to take what you want and make the game you want to play (aside from setting information.) Original Dungeons and Dragons was made to be modular. A GM could take rules that he or she felt made a good game and expand on them as they wished. With D20 if you take something out there is always a fear that the tower will go tumbling down.
I prefer to play my games with a certain amount of give and you-can-mess-up-ness. I like to get to a point where I can go. You know what my character is changing or hey we are in a different environment and I need this new skill. So for me 2nd ed is the better choice for Dungeons and Dragons. I really don't have a lot of fun with D20 systems.
*Munchkins are a term for players who try to make the "best" character in a competitive manner. Usually this involves downgrading certain traits to make others better (known as minmaxing). Many of these players think that one type of character is superior to others and are interested in "winning" a game that at its very core is a cooperative game.