Greetings, Syn. I checked out your guide, like you asked me to, and here are my thoughts, as requested.
Slug - Excellent attack. I use it more often than any of the others.
Burst - You are correct about it losing some effectiveness in the later levels, but I still use it almost as much as slug. It makes a good finisher.
Buckshot and Grenade - I got rid of Buckshot early on, because I found this power simply did not do enough damage, and the knockback was too random for me. I like crowd control. As for Grenade, this is a thoroughly wretched power. Nothing like hitting your enemies with a GRENADE and having it do less damage than a single bullet.
Sniper - I LOVE this attack. I almost always use this as an opener. The way I have it slotted makes it very effective when fighting all kinds of villains. Nothing like taking out a villain in a few attacks because of this one opener. The only thing better is LRN Rocket from the epic power pools.
Flamethrower - One of my favorite attacks. Great for crowds.
Ignite - I still have difficulty understanding why people hate ignite. One immobilize/hold + Ignite = Easily killed LT.
Full Auto - You are correct about Full Auto getting slammed in I5. However, it is still a great attack, and as long as one is careful, the long animation will not become a liability.