It's a very decently designed MMO *Yes, MMO* FPS. IT's not a lobby based system unless you're launching into the various elements of the game. Plenty of PVE, Plenty of PVP, Daily missions, weekly resets to make it feel truly MMO. The only problem is the way they chopped up the game to release the DLC, because some stories make absolutely no sense and they introduce too many enemies way too fast and try to make you understand their storylines with little to no backstory, unless you log on to Bungie.Net and read the grimoire cards (which actually tell the lore of the game). With the lore (if it was included inside the game) it could have been a masterpiece, but people won't log out to read them unless they are hardcore fans like myself.
That being said the lack of content makes me play it rarely - I'll cap out my Nightfalls/Weeklies/I'll use Zur for Exotics still on Friday/Do the Raids for Lockout timers/ and cap Vanguard/PVP Marks on each of my three guys. This usually takes up for 4 of the 7 days in the week, so it's easy to enjoy it spurts or whenever you want. Casual Hardcore player lol.