I'm not sure if Sandy would ever get over the experimental phase. He churned out ideas and concepts and I'm pretty sure he was behind some of the new linedef actions. Plus, he's credited with map07 and map30, so he had his fingers in the hardcoded bits as well. In my opinion he'd just bother Carmack with new features and hacks forever, heh.
I wasn't just talking about tech limits, actually I didn't real phrase it well. I meant it felt as though Sandy never got chance to get past the experimental early phase of mapping where you want to cram in your cool ideas but don't yet have the technique to execute them quite right (if it is based one one gimmick) or make the map a cohesive whole (if it was several). I'm sure given more time he would have but we'll probably never know.
Now I think about it this really only applies to Petersen.
What his maps do lack is polish (duh) and also certain layout dynamic that Romero mastered and McGee simply stumbled into because of his stringier layouts. Sandy did separate trapped rooms with lots of pace breakers like elevators, switch-operated doors, crushers, teleports. His monsters are revealed or teleported only after you get somewhere or do something... It's about scenarios, puzzles and surprising the player, not about putting him under constant pressure with well thought out monster placement and dynamic fights. Maybe that subconsciously grates on some players' nerves.
Oh and while I'm ranting, let me address this silly notion permeating this thread that Doom 2 had only one new weapon. Nope, Doom 2 was the game that truly introduced the BFG. It appears very late in the OG (E3M3) and if you pistol start, you won't even get it in the map that'd let it shine the most (E3M6). Dropping packs of demons in Limbo is fun, don't get me wrong, but you never have to rely on it and it utterly destroys whatever danger E3 presents. There's one scenario in E3M5 where using it is truly justified, but other than that I can think of just the cyb in Warrens and that's not something to brag about. Everywhere else the hallwayish, maze-like layouts of Doom work against the strenghts of the BFG and you struggle to herd enough monsters together to justify the ammo loss. With the exception of baron takedowns, plasma or RL does the job more economically.
Nerfing the SSG might actually cause you to switch weapons. You really don't have to in its current state.
Now enter Doom 2. Sure, you can kill almost everything with the uberpowered, omnipotent SSG, but you don't really do that, do you? Not when the game is riddled with BFGs and cell packs to destroy wonderfully grouped hordes of meat! The introduction in map08 clearly indicates that. You do switch away from the SSG all the time, don't lie to yourself. There are 20 SSGs and 19 BFGs in the whole game on UV. Doom 2 on continuous is most definitely about juggling the SSG and the BFG and both is very gratifying. The bigger and meaner fights are certainly handled much better than any mass murder scenario Doom gave us with its "mow down the zombies" and "one hell monster at a time" approach. Doom 2 introduced the BFG as we know it.