I recommend this game, but with a huge caveat. How much do you really
enjoy retro platforming?
Everything about this game is very well done: graphics, the Heavy Metal magazine heroine, and the fantastic soundtrack. There's even a good bit of replay value, which isn't always the case for platformers. The gameplay is... well, "retro".
If you've never experienced actual older games, or you tend to forget how many of them actually sucked, I recommend watching a playthrough of a game called Phantis, which this game is basically a remake or spiritual sequel of. With some exceptions, older platforming games often had slow, sluggish protagonists, with fast, incessantly spawning enemies, with awkward jumping and shooting controls. This game is no exception.
Serena walks slowly. She has to stand still to shoot. There's a small delay both before and after firing the actual projectile. She can only shoot up at a shallow angle (perhaps 30 degrees), but not straight up. You get hurt from touching a robot's toe or a wizard's robe. Additionally, the delay in firing means that if you try shooting just before you land, you won't fire. Even her ship takes a moment to accelerate to full speed when moving up or down. None of these would be a huge problem by themselves, but combined, it can lead to some very frustrating moments.
Everything else about Ultionus is improved over the older games; why not tighten up the gameplay too? There are also plenty of other "retro" games that actually have really great controls.
As I'm sure most can agree, it's more fun to challenge the game, not its controls. But if you love punishing gameplay, repetition until perfection, or just love all platforming games, then it's hard to do wrong by Ultionus. Even better, it's very inexpensive.