Whiners everywhere
Why is everybody whining about the controls? if you're a PC gamer the setup is the same that's been used for ages. I, myself, had zero problems with it, except that my pinky got cramped after playing for like 6 hours (although I didn't use my pinky). And I guess HecticMuffin didn't play past level 15 because W is used to go up ladders and you can jump off those, which is critical in several points. Mapping jump to W is a BAD idea.
Loved the secret weapon, it's great fun at the new beginning.
More general aspects. Well, music started getting on my nerves after a while, but turning it off solved that.
-All the guns were good when you first got them. But by the end it was pretty hard to get the last weapons because gems are really, really scarce, or at least they were in my first playthrough, I couldn't get the microgun.
-A map would make navigation easier, even if most of the time it's pretty straightforward if you keep your eyes peeled. I got lost more than once and it was pretty frustrating to kill the same ghosts over and over.
-Difficulty was fine, IMO. Some mobs were very tough, but they all exploded in the end. I had nearly run out of bullets when the final boss killed me, I made sure to restock plenty ammo.
-I really missed a lot of stuff, some of the breakable walls were incredibly difficult to spot, and then even harder to break. Dynamite was rare at the beginning but then I was swimming in money and hence explosives. The grenade launcher was a great replacement for dynamite but it came a little late for me. Bigger cracks on the breakable walls would have been nice, or maybe a weird sound like in zelda.
I thought this game was awesome, one of the few that grabbed me enough to play 6 hours without rest until I was done with it, and then start again to get even more stuff.
And as final thought I really hate water and lava.