Sorry for the incredibly late reply but I was hoping to release an update to the game at the same time.
Weapon power ups: each weapon power up just gives you a bit more ooomph when fighting back. I guess it doesn't really matter what the weapon power up actually is but they go from normal - fast firing (but overheating quickly) - fast firing (& better cooling) - faster projectiles - anti mothership. If you do very well and get to 200K then even better options appear above - you get nukes, super cooling for your weapon and shields that will turn on automatically if you're hit. Managing your power ups (ie getting the right power ups) is vital in the game.
At the top there's also the info showing when a mothership is coming or if a little green alien is about to be dropped to the ground or if the grey motherships will stay on screen after you kill everything else. I find this info vital as I like to plan how I'm going to destroy the wave - firing wildly gets you so far but I find a little planing helps if you want to get a decent high score.
The time bar is useful as you get a fine if you don't clear the current wave in time. You also get a bonus if you clear them before a certain time (shown on the time bar). There's also a heartbeat sound to tell you when you're running low on time. Do you need the time bar? probably not but it looks pretty.
The weapon heat bar shows you when you need to stop firing and cool down - it's obviously bad to get stuck in a fire fight with the little green guys if you weapon is already overheating. The turret on your ship starts to glow red when the weapon overheats so you can use that as an indication if you wish. Do you need the weapon heat bar? probably not but I find it useful.
Do players need any of this info? No. Does it benefit them? a little. Does it look interesting on screen? I think so and the main aim of any arcade game is to look as attractive as possible to entice the player to play. As players get good at the game then the info becomes more important. At the end of the day, it's a bit like the rev counter in a car - I never look at it but I'd feel something was missing if it wasn't there
I have released a totally new version of the game just now. I'll try and remember what all the changes are and list them down. Thanks for playing and all feedback is welcome.