Well..
I was enjoying the game, not quite loving it. But liking it. And then in the level after I got the shield OMG glitch. Wondering what the glitch is. Well it seems to work in harmony with lag (I think). I think the game started to lag, and although the enemy movement speed slowed they kept firing at regular intervals which made the game lag even more. My ammo moved fired at it's normal rate so for every shot I fired the enemy fired about 20. And I was using the fully auto gun. So it kept getting worse untill ultimately there was nothing on the screen except enemy shots and the explosions where they were killing me.
The odd thing is that although my movement was impared my ability to control when I was firing and to turn on my shield was not.
Anyhow the bug/glitch was bad enough I didn't bother starting another game. So it is goodish, not recommended if you might lag.