Space Run is a tower defense game where enemies go to you as you're flying a spaceship trying to deliver thing under time constraints. It's a fun game where the tower defense gameplay loop of having a list of things you can build allows you to complete maps not perfectly, but well enough to buy better things later on in order to go back and finish stuff you couldn't do before. It's also very interesting with the way it deals in tower construction and enemy waves.
After loading necessary cargo on your mission-by-mission defined shape of a spaceship - the cargo is usually a single reactor and some crates, although some maps will require you to haul people around, and they have special needs - you start flying at the output your rockets gives you - the ones you start with propel you at 100 units per second. Then you use the hexes on your ship to build new modules, lasers, missile pods, shields, reactors, more rockets, and much more. After you get the cargo to the finish line, you get paid and you get reputation. You get more reputation and money if you deliver all the cargo and if you deliver it really fast, usually by building more rockets on your ship.
During the travels, your path is crossed by meteors, pirates, competitor ships and giant boss fights. You get warned way ahead of time and you have the ample opportunity to rotate certain parts of your ship around, or to place shields, or to build new defenses to deal with the incoming danger. Enemies have special properties. Asteroids will just slam into you, some more advanced foes will shoot rockets at your systems, some have shields. The only issue I have with the game is how you can't fast-forward the time, nor slow it down. It's okay to know that there will be a bunch of enemies in 30 seconds, but I don't really want to wait that 30 seconds, I wish I could just press a button to make time move faster, like in most tower defense games. Destroying enemies net you currency to build more towers and to use special abilities.
Towers have neat abilities, some are free - like being able to rotate turrets once placed - and some cost some currency - like the rocket launcher's 'wide angle' ability. You can repair most structures by default when they're not actively being hit and you can also recycle most of them. The way you place them on your ship is a bit puzzle-like because they have certain requirements, like one or more free space outside of your vessel, or a reactor nearby. Reactors provide energy that can be passively used to boost certain parameters of your structures - shields upgraded to max will take 50% damage less if they're nearby a reactor - and to use active abilities, like shooting faster for X seconds.
I never had a bad moment with Space Run, it's cool tower defense concepts applied to light ship building mechanics with the feel of puzzle-solving you get from well thought of tower defense games. It's also full of charm and the atmosphere is pretty cool. Try it if you like that kind of game!