For one thing, yeah, having the anime end on a weird note so you have to read the manga is pretty lame, but sometimes that happens. I think Shaman King ended like that in the anime (I don't know yet, haven't gotten around to watching it), but considering the manga did end up ending on a strange note anyway until it was picked back up... I'm sure there's one other show out there that did this similar to Soul Eater... well... didn't the Trigun anime end on a midway-point with the manga, if I read up on it correctly? Even then, the anime still had a great, satisfying conclusion, so either way, when they adapted it, they wrote it in such a way that it would end on a good note, yet keep a slight ambiguity. I personally like that in most shows if that was the style of it to begin with.
Well there is a bit of a difference. While there may have been more story in the Trigun manga, it isn't really necessary for the anime. Now you want a show where the manga is necessary, try for season three of The World God Only Knows. Or the original Berserk anime where it literally just cut off. If they can give a satisfying conclusion and at least wrap up what they have introduced, an anime can be only a section of the manga it is adapting. Also, like I said, Soul Eater didn't require reading the manga, I just really disliked the ending.
As for Evangelion, remember, they were running on a tight budget. The last two episodes happened because of money problems, and also because I think the networks wouldn't air the true ending (which became End of Evangelion, and thus is a better conclusion--though some fans will tell you otherwise). Honestly, the TV ending doesn't bother me, and it was rather thought-provoking about the series. It's still a bad ending because it's more of an "easier said than done" ending, to say the least, but it does fit into the continuity of the show, in some ways. Either way, the characters remain mentally broken, one ending just has a more... disturbing take on it than the other, yet it really does end nicely.
I won't deny that they had monetary problems, and probably some production issues. But that also applies to The Thief and the Cobbler (Minus about 30 years), and that is still not a good movie. I understand that it can't be helped, but that doesn't make it good.
So sadly, there's nothing we can do if an anime has a bad ending because we have no control over the adaptation, budget, and ratings (which all come to play in some form or another). I honestly haven't run into a lot of anime that end on a bad note, and even if they did, unless the show itself was bad, they don't necessarily bother me. I mean, for one thing, I may not know of the manga to begin with (which probably helps my personal enjoyment so that way I'm not fretting over various things such as "How are they going to do such-and-such, this-and-that?"), and the other is sometimes they do foreshadow what the ending is going to be like. Sometimes they don't, but if it fits well-enough into that particular continuity, I'm not going to complain.
Not going to argue with you, you do have a point. But I personally find the ending a very important part of a show that should help tie things together and bring it to the end. When a show has a bad ending, it can taint my entire opinion of the show. All personal opinions and conjecture at this point.
Well... the anime adaptation of Majin Tantei Nougami Neuro ended weird, but I still enjoyed it, even if the final arc or two felt a bit out-of-place. But that's as close to a complaint I have when it comes to this sort of thing.
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