It's not bad, but it's not good either. Yes, it has a 'retro' feel about its simple gameplay and yes, it has good controls, but it's just too bland to be fun. You shoot things left and right (literally), gather crystals and sometimes carry things to a gathering point. There are platforms, but they are just horizontal lines that stretch through the whole 'level'. You get weapon upgrades and unlock spacesuits over time. That's the game. It's very repetative and while that was fun in Pang over 20 years ago, it just doesn't hold up today (plus Pang at least tried to put some effort into giving you some motivation).
If you look for a very simple shoot 'em up this might be for you, but in general I think it doesn't offer enough to hold your attention for more than 15-20 minutes.