In case your haven't noticed like I have, Kongregate members usually like games that are easy over games that are hard, its one of the reasons a lot of my games don't score well.
Can't satisfy everyone you know. I lowered the difficulty on some bosses, but many people still find it to be a challenge, especially the last few levels. That means its hard enough.
I lowered the power on some of the bosses because of complaints, some savegames may have been lost, but they should be re-gained after you've beaten any level(go back and beat level 1 if you want).
You can kill all the Bosses, they just have quite a bit of life. As for the 4th Boss, yeah, you can kill him. Try getting triple shot and boosting the attack power of the cannon.
I uploaded an update version with the multishot as the top powerup you can get. Save of the savegames might have been lost, sorry. Get the Multishot, it is the best.
Ok, I fixed alot of stuff. I gave the hotel more HP, made re-load by "R" take a bit of time so you can't just hold down "R" and shoot forever, grenades are not free and a new sound for the shotgun.
I just checked the I-phone version. I bought this game(exclusive source) for one of the developers off of FGL, the flash version completely belongs to me now.
 "Super Castle Quest: part I")
 "Lone Space Defender")
 "Hotel Defense")
 "Warzone tower defense")
 "Glass Tower")