Nope. I just like seeing things end regardless of the ending. To me, it's how they got there that counts. There are titles that would make me want to stop watching to take a break from heavy emotions [Clannad -After-] or make me want to stop because its boring or disgusting me.
In Guilty Crown's case, there are things I didn't like, but the optimist in me looks for what's good in a title. GC is one of the titles written to depress in the later half, which it did well.
What's good in it? The soundtrack is one thing, the first half is another. The second half did its job, so I think that's also good.
I stopped a few days when they implemented the ranking system and an angel died. I finished it because the optimist in me was looking for some sort of redemption in the later episodes and there are, but it's one of the titles I might not pick up again in a while unlike the titles I really liked.
There are titles that are bad or a waste of time, but there is no such thing as a title that is not worth watching or finishing.
Now this is role reversal.
You are far more charitable than me. I do not drop shows often, but when I do it's when they have pissed me off to such a degree that there is literally no good point which can redeem it's glaring faults (and even then I don't always drop it, as by the time I grow to hate it with a passion I'm often too far in and I figure I might as well just finish it, which was the case with Blood-C).
I've heard with multiple people that Guilty Crown's second half is better, but the 1st half just pissed me off to such a degree that I could literally care less about what comes next and I don't care at all about what I'm possibly missing. You mentioned Clannad, which is an Anime I love myself (both seasons as well). Sure, After Story was depressing but I already loved the first season and After Story was of excellent quality as well, so I kept going regardless. To me there is a gulf of quality difference between Clannad and Guilty Crown so great that saying it was the difference between McDonalds and Wagyu Beef would still not come close.
I'm sorry I'm being so harsh, as you are obviously being far more open than me. I do respect that you like to see your shows to the end, and It's something that I try to do myself. Guilty Crown for me however just pushed my limits too far, and to anyone who watched it to the end on the principle of finishing what you started, props to you. You have a level of patience when it comes to Anime even I don't have.