I once described NGE (eva) as a 15 course Japanese meal, with each course ranging from the food of gods, to dire tripe that even dogs wouldn't touch, depending on your taste. There in lies probably the greatest problem, while it isn't really a lack of concisancy there seems to be lacking a certain something to bind it together. There are 4 semi distinct phases of the series and each has its highlights and low points. The 1st phase is Shinji's arrival and his... adjustment period. Its very physcological, deep and an in depth look at shinji and his troubled mind. The second Phase starts with the arrival of Asuka and is a much lighter phase, also it is when a lot of the sub plots start. The Third phase strats with the arrival of the Unit 03, and is when the midden hits the windmill (like the **** hitting the fan but on a bigger scale) and things get dark... REALLY dark. No one is a happy bunny and things get a little wierd (freaky weird, not funny weird). Tears down a lot of what has gone before. The final Phase is those legendary last two episodes (or two movies) the series ending is ... no point trying to describe them, they are wierd (WTF!!! weird, with the three excalmation marks). While the movies are more mainstream they still are weird (WTF!, note only one excalmation mark).
The series is worth watching, but i would strongly suggest trying it all before buying, as it does change as you go along and you may not like what it changes into.
Would suggest watching Raxephon before Eva, but mainly as i would like to see what you think the two after watching them in the reverse order than they were created. Since most people watched Rahxephon second they think it is a rip off of Eva.