On a Roll is a 2D platformer where you control a ball/circle character and proceed through linear levels. There's a good deal of platforming (in the more standard running/jumping sense), despite the presence of rolling. You spend time bopping on top of bad guys (other circles) and avoiding the standard set of hazards (i.e. pits, spikes, etc). You also have the task of collecting stars that are scattered strategically around the level. Collecting over one hundred stars allows you to be "hit" once at which point you lose 100 stars. So it's ideal to collect as many stars as possible because for every one hundred you have, you can take a lick and keep on ticking, errrr rolling.
Graphically, On a Roll looks good - crisp and colorful. It can feel a bit flat sometimes, which might be more noticeable because we usually think of rolling objects as spheres/balls and these guys don't really look spherical. The levels themselves sort of follow suit - they are well designed and paced well but can be a little repetitive because of the fairly simple image sets.
Cutting right to the chase, the rolling element is fun and well-executed. You can shoot up walls and around loops at any speed. You also can stick to ceilings which allows for some pretty flashy high-speed rolling. At one point, I thought speed and momentum might be needed to stay "on track" but On a Roll allows you to stick to essentially any curved wall no matter how fast you're moving. I actually like that twist because it allows for more careful rolling when it's called for, but it does come with a drawback.
That is, the controls seem to be affected by the ability to stick to any curved surface. So while rolling performs nicely, the jumping/platforming element can feel frustrating. It's almost like the character is magnetized to the walls - it's very hard to perform jumps because it never feels tight or accurate. It's difficult to explain but if you try it out, you'll notice what I mean. And you can't leap from any curved surface, which means there's really only one thing to do in those sections....roll. After about an hour of play, I felt as though level progression consisted of roll roll roll (easy), and then jump jump jump (frustrating deaths) - rinse and repeat. The awkward jumping irked me.
On the upside again, practicing helps and I did get better at dealing with the odd jumping pull/push. There are some little touches like choosing from a selection of color schemes for your character and boss battles (although they aren't anything breathtaking, they do mix up the action). It's also quite challenging to make it through full levels (levels consist of sub levels) with the 3 lives you're given, so after about 2 hours of play I still seem to have a ways to go. You have to be very careful at the beginning of the tougher levels because you essentially can't make any mistakes or it's a quick death. If you patiently collect stars, you afford yourself some breathing room.
I'd recommend that any platformer fan give this demo a try - especially if you get a kick out of the rolling element. At 240MP, that feels like the right price.