Title says it all. Magic Barrage is like Realm of the Mad God on steroids. SO much more loot options and character customization its crazy! Try out the game at http://magicbarrage.r2games.com/ .. Its awesome!
I've gotten to 31 in this game at the moment and I think it's actually pretty neat. It's a more long-term game than Realm of the Mad God so it has a very different feel; it's less hectic and it's more solo-friendly, but you also won't see all the content it has to offer in a single day. Basically, it's a nice alternative for anyone looking to have a long-term bullet hell mmorpg rather than one which you play in short bursts here and there like RotMG. It does seem like it needs more content (it starts running a bit thin in the 30's and the cap is 80), but it also just launched so that will probably get patched up as time goes on.
Otherwise, the only real downsides are that the UI is a complete mess (buttons and submenus absolutely everywhere) and it really throws the Cash Shop at you a lot (that being said, the Cash Shop doesn't seem particularly overpowered as the focus is mostly on things which make you progress faster; there are lots of 'costly' things around the $1 range like double exp and fatigue refills and tons of tiny things worth the equivalent of $0.02-$0.09 like 'lucky wheel' spins and inventory slot expansions).
In terms of fun, I'd say RotMG is the more enjoyable of the two, but I've still had plenty of fun with this game and it has the benefit of long-term appeal. I'd say it helps a lot to think of this more as an additional game in the sparse 'bullet hell mmorpg' genre rather than a RotMG clone because the two games approach the same formula in two very different ways.