I do prefer the game system in AD&D3 to that in AD&D2. I can see why they used it, but to me, THACO was always a non-obvious concept.

However, one thing I do regret about moving to D&Dv3 is the loss of the D&D2 Monster Manual. I considered the D&D2 monsters to be much better. For example, why in heaven's name did they omit the Cave Fisher from D&D3??? It could be used to add variety to virtually any underground dungeon or cave system of medium size and up. Not to mention low-level beasties like the Crawling Claws - just the thing to make a jaunt around a haunted castle more interesting for a relatively inexperienced party. And what happened to the Bone Golem? A couple of those hidden in a pack of skeletons made a very nasty surprise for a careless party (one that didn't bother to carry out a "Spot" roll), or an unlucky one that failed it when they did so. Or the Glass Golem - who would suspect guardians of the treasures in a Church Sacristy to be watching from the stained-glass windows?

Instead, you have a slew of new monsters who are too fantastic for words such as the Gibbering Mouther or Ethereal Marauder, or ones with disproportionately powerful attack, such as the Bodak. I don't mind killing a player character when acting as DM, but only when it is merited. I abhor including monsters that kill a healthy PC via a single dice roll if the PC fails (say) a Fortitude check. Likewise, I won't take part in a game run by a DM whose objective is to kill the PCs.