ok I've just watched the eureka 7 film and I'm like, it would have been ok if I hadn't seen the series. Surprisingly I wasn't as badly disappointed as I was expecting to be too.
Now I'm a huge fan of e7 series and rate it as a top 5 type anime so I suppose I was one of the people that the film was aimed at. The problem is that its not e7 enough, they've got the same characters but they're different personalities and considering it was the people that drew you into the story of e7 then thats not a good thing to do.
I can understand why its been done in the way it has (its explained about half way through and I'm not going to go all spoiler on you) and if you watch it as a separate entity based on this then it works fairly well in that context.
I'd also say that if you go into the story expecting a re-imagined series of the original then (think fma etc) I think you would be wrong to do so as I'd class it more as a side story due to the above.
If you've watched e7 then realistically you are going to watch it and I would recommend that you do actually watch it at some point, the re envisaged nirvash is pretty cool although maybe lacking some of the elegance of the series version.
Plus it was rather entertaining trying to spot the bits which were ripped straight from the series and the end style/image of eureka was nice too
If I was to give the film a rating out of 10 I'd say a 7 with the series being one of my few 10/10 series. If I hadn't have seen the series then I suspect the film could have been a 9/10 maybe even a 10/10.