Galaga Legions DX is purely an arcade shooter. You begin as a meager ship and as enemies encroach, you shoot them, recruiting some to your side, clearing the level. As things get more intense, the enemies will grow in number, complexity and difficulty, but your ship will also level up and have satellite (previosuly enemy) ships alongside it to assist, so it all sort of evens out.
You can choose to play the Championship Mode or play individual areas, of which there are nine total, tweaking the difficulty for each, as well as choosing your preferred visual style. There are five different levels, and you will go through a number of waves of enemies per level. You will have a time limit in which to clear the waves, but even when I didn't quite clear the last wave completely, I still seemed to progress, so it didn't appear to matter much.
Aside from playing through the Championship Mode (which doesn't take too long), and clearing individual areas, you can also choose Tutorial or Time Attack. Tutorial is a great place to start, because it offers lots of tips and tricks to quickly clearing levels and it identifies problem areas in the levels. Time Attack is similar to Championship Mode, but you will have the chance to beat your best time, and if you don't complete the levels in the given time, the round ends. Lastly, there's the Champion Score Attack Tournament, which had closed at the time of this writing, but should re-open soon for those who want to pit their scores against other online players. The online requisite Leaderboards, however, are always available for you to check.
Don't expect a world of variety in Galaga Legions DX; you shoot little alien creatures that attack you - it's what you do. Some may be more difficult to kill or more crafty in trying to kill you, but it's just a lot of the same. That's not necessarily a bad thing; I am just letting you know. That being said, you can play each level on each difficulty and it ends up being a lot of levels, but they all just seem the same after a while. Once you complete a level, it brings you back to the area select screen where you can, once again, tweak the difficulty and visual style type, but I do wish you could just blaze through each level one after the other, starting on the easiest level of difficulty and working straight through, but you can't. You can work through all of the areas on Championship Mode, though, so that's good.
Lastly, Namco Generations is avalable for you to check out the latest information on these classic revamped titles, like Pac-Man Championship Edition DX. There's a section with updated content, as well as the option for you to download the demo for Pac-Man.