Did Abin Sur not make the prison good enough to hold Parallax forever and how was Abin Sur defeated so easily?

The Green Lantern movie is only very loosely based on the comic book series. As opposed to being imprisoned in a prison of emerald crystal in the movie, Parallax was originally captured in the Green Lantern Central Power Battery as the yellow impurity. He then escapes from it to wreak havoc.

However, none of that happens in the movie so we can only speculate. The prison he was in was created by Abin Sur. Seeing as only Abin Sur could stand up against Parallax, he must have been very powerful. His prison would have been even more powerful to hold him. As with all Green Lantern things, it's only as strong as the willpower that drives it. It is possible the willpower of Abin Sur had diminished since the time he imprisoned Parallax. While it originally was strong enough to hold a powerfull Parallax, it is now weaker and, apparently, weak enough for Parallax. Parallax's powers also weakened (as he was there for quite some time without anybody around to give him power) during his captivity which is probably why he could only escape when the astronauts were there.

Could Abin Sur have used eye patches? Perhaps, but there might have been better things that were no longer there.

I mentioned that Abin Sur's powers could have diminished since he imprisoned Parallax. This can be found in the comic books as Abin Sur had heard of the Blackest Day prophecy. He then started to use a spaceship while all Green Lanterns could easily travel using their power rings. As Abin Sur no longer trusted his resolve and feared the prophecy and Parallax had the advantage of catching him offguard, he was able to defeat Abin Sur.

This question depends on which side you want it from, the movie reference or the comic canon? In the movies it is not really explained but from what I can gather Parallax had been feeding off the organisms fear each time they came in close proximity. Then when the astronauts crashed this was the last bit of fear that he needed to escape, by this time his power had grown to match Abin Sur's which is why he was able to escape. From what I can gather he then went and fed on others fear and became more powerful, so powerful that he was able to defeat Abin Sur. And because his power can grow each time he feeds on fear, and because Abin Sur was not ready, a bit out of practice and his power had maybe diminished a little he was defeated. Although I still think that he was one of the greatest Green Lantern's as he was not scared and still had the Will to fight back a little whereas some of the other's were fed on later on in the film. Abin Sur lived long enough (with a hole in his chest, not many could do this) for the ring to find a new member.