Too many problems.
First off, this is no sequel. It's a completely different game, you should give it a different title. I'll start by addressing the good/bad parts of each weapon.
Mobile gravity manipulator: It's a nice weapon, but it's hard to use early on because of the lack of control after they hit something, and the fact it is difficult to damage anything with it in the first map. In a good map and with the right upgrades, it becomes fun.
Gravity disc: Hey, this thing was fun with the right upgrades. A little slow at first, but then it became one of may favorite weapons. Until I came to a level where each time I used shockwave it would go off screen, no matter WHERE I fired it. Frustrating.
Singularity cannon: I liked it at first, it gives a unique playstyle. However, when I came to the "disadvantage" level, where my cannon was placed in an area prone to suicide nukes, it got frustrating, really, really fast. What was I supposed to do? Max shield wasn't going to protect me from a nuke, my primary weapon DREW THE TANK CLOSER TO ME, my secondary weapon didn't push it back at all (it really should) , and my homing mines DIDN'T TARGET IT, and prefered to hit other targets, causing explosions that sent the nuke tank flying into me.
Artillery: Honestly the worst. It wasn't fun trying to predict where the tanks would be EXACTLY. Predicting where 20 tanks will be after an explosion is even worse, I would set up some shots but a tank would unexpectedly explode, sending the others out of my range for my shots. It was easier to just set up lines of explosions for where the tanks COULD be, or just send in a nuke for every group with more then 4 tanks.