When first unveiled : 7.5/10.
Sure, it was all concept arts and empty promises, but it legitimately felt like something large and exciting, but as usual, keep expectations tempered and that don't be too gungho on something without in-game footage.
Period of first gameplay reveal to first few months of console launch : 7/10
It was starting to become clear at this point that the foundation of the game was already there, and that it was going to be an MMO-lite. At that point, it felt clear that Destiny was going to not going to come off the gate with everything teased or promised, with some of the things talked about in their unveiling being left for future games, like ship combat, etc. Or a ton of vehicle variety, etc. Still, the game looks nice, there's a directed storyline, etc.
Impressions of poor MP experience, alpha leaks and the not-so-impressive Strike mission demo : 6.5-7/10
I still think the game was going to be great, but the first showing definitely raised some concern that the gameplay might not be as fun as hoped, probably losing some of the directiveness of a Halo SP experience in favour of a more MMO approach to enemies.
Alpha : 8/10
My biggest concern for Destiny was elevated by the alpha. Personally, I was already ready for the possibility that the first-game is probably going to not be 'extremely' content-rich, but regardless of whether or not that is true, the alpha reassured that Bungie's foundation with the game is very strong, and that beneath everything else, it's got an immersive fun gameplay experience that's already very enjoyable even with the limited alpha content.
I will say this, in that I think Destiny will be this gen's Assassin's Creed 1, in that it was a game that establishes many strong foundations, but probably not as 'complete' as it could be, but the foundation is very strong in that its sequel took to the next level and beyond. I think. If Bungie suddenly rocks my boat by showcasing half the solar system explorable in the first-game, I'd gladly eat my hat, but right now, I'm expecting a big game with a lot of things to do, but also not as big as hype might portray.