I posted some opinions previously, and they were pretty negative. Since it's free to try at this point, I poured about four more hours into Destiny today, doing random missions, the Strike and PvP.
After about five hours, I think I'm finally starting to understand this game. If your initial impressions were as bad as mine, then give the game some more time, and definitely group up with others. This game is meant to be played with others. No question. For anyone on the fence, having friends to play with makes the game instantly better. I only played with randoms, none of whom used mics, but it was instantly more enjoyable once I grouped up. Playing this game solo is going to create a fundamentally bad experience. Don't even bother trying.
Despite this, Bungie make the mistake of setting the roster default to "Friends" only. Change your roster to "Public". The game instantly becomes better being able to group up with randoms. Its also worth noting that the game is experiencing bugs where you won't be able to see other people at all, so using this Alpha as a metric for the final game won't work if you're encountering the bug.
Anyway, Destiny is a lot better now that I've spent more time with it. Approaching it as a "shooter" is the wrong way to play. Its an MMO first and foremost, and has its own unique style. Once you approach it correctly, and play it as an MMO, things start to click together, and Destiny starts to work. It takes a while to find the groove.
Combat is simply a mix of ducking out from cover, using the environment to break LOS, ducking into cover when you need to reload, and timing the pauses in combat to recharge your shield. Its less about your speed and skill with shooting, and more about tactics and gear. Forget what you think you know: the usual FPS plays simply don't work here. Circle-strafe is all but worthless unless there's only one enemy. Jump-shoot is almost entirely ineffective. Sprint-reload doesn't work. A liberal mix of ADS and from-hip is needed, to keep your mobility high.
Also, the "Boss Health" issue isn't an issue with the Bosses, strangely enough. It's a weapon issue. Most players simply do not have Heavy Weapons, which deal massive amounts of damage to the Boss' weak spots (give yellow damage). The Spider Tank takes around 25 minutes to kill without Heavy Weapons. Its a fucking joke. In my second play of the Strike, I had a Heavy Weapon, though my two buddies didn't. A typical RPG kinda weapon. This time, we did it in about 7 minutes. Heavy Weapons, man. If you have a Heavy Weapon, hold Triangle to actually use it, rather than just pressing triangle. They also make facing off against those Knights and Captains with Shields much easier, due to their massive damage.
The PVP is kind of shit right now, frankly. Not responsive enough, even by Bungie's standards. The balance is fucked, too. Players don't begin with Heavy Weapon ammunition. This means vehicles rule the map. Whoever has the better pilots, wins. No contest. They really need to fix this, makes it virtually unplayable.
Also relying on your PvE gear is terrible. Weapons seem to do the same damage in a class, ignoring their stats. I imagine players will have PvP and PvE sets of gear. I hope Bungie add an "auto-equip PVP Gear" thing, because it'll get really fucking tiring swapping sets out. Trying to use a semi-auto rifle in PVP is impossible, whereas a simple shotgun is a fucking killing machine. Horribly unfair.
My earlier comments about the sterile world and lack of story still stand. The game lacks any and all context, and the world is utterly empty of anything relating to story. I'm not just talking about the Alpha, either. I mean the world is just... empty. Enemies are just there. Building have little in the way of context or purpose. Even the Strike failed to tell anything resembling a story. Its really, really weak, and what is there is horribly boring and generic. Disappointing on all fronts.
Overall, though, my opinion has improved dramatically with more time. Learn to play it the way Bungie designed it, instead of like a normal shooter, and it gets a lot better. It's not all good, though. Bungie's terrible story telling, mixed with Peter Dinklage's character, nearly ruins the entire game. There's just so little to actually see in Destiny that its really hard to push on without the progression. Having hit the level cap, I'm done with Destiny till the beta - there's nothing worth revisiting for the sake of it.
I won't be pre-ordering, and I'll wait for the beta before making a purchase decision. The story telling needs to pick up A LOT and the PVP multiplayer almost needs a fundamental re-do before this would be an instant purchase. Its alpha though, so there's time for them to address all of the issues. I hope they do, its very interesting, and has lots of potential.