I loved that you spent the time to add a tutorial level, very nice. I also liked the artwork and was amused at having kicking press buttons, nicely done. I must admit, I'm no longer the FPS player I once was, and these bugs did kick my ass.
I too experienced a noticeable load pause the first time I used both the shotgun and the grenade (playing on web using Firefox), and I suspect the VFX or sound FX is being demand loaded. If you can work them into your load screen (either hidden or otherwise integrated) it shouldn't be seen mid-action. The only other thing I could wish for is some slight color variation or pattern variation in the walls to help give the user more depth perception when moving about when there are corners (the eye will more easily sort the smaller patterns as further away).