Made the mistake of buying this first before Dodonpachi Resurrection HD. I am a huge Phoenix HD fan, which I feel mixes the classic pace of games like 1943 (arcade) with more of a Dodonpachi bullet hell style…landing in a nice spot between the two.
Anyways, with that preference and style out of the way, Dodonpachi Maximum is a strange game. It's not as satisfying as Dodonpachi Resurrection HD, which is the "instant classic" you should definitely buy first.
DDP Maximum makes a good second game to get after Resurrection…if you can finish that game. Phew. Either way, I am stuck with both and actually quite happy. I do play both.
Also: if you are "worried" about the lack of iPhone 5 capability on Resurrection HD and favoring this one because of that…don't. This game leaves your time and network name bar at the top (instead of true fullscreen) and the window itself has a border around it, just like the other DDP games out there. The differences in "actual" play area are minimal.
Anyways, once I bought this and was not thrilled with it for my first Cave shooter, what I did was try out Espgaluda II, DDP Resurrection and Deathsmiles…personally realized I was having the most fun with DDP Resurrection, so I bit the pink bullet and bought that. Happy with the two, but if you can only get one, get Resurrection.