To review, this game started out as Keep on the Borderlands, though I threw in Tower of the Stargazer, Wizard's Challenge, In Search of the Unknown, and a couple of dungeons of my own design as well. I run it sandbox style.
My players are all new to D&D. For two of them, I am their second DM and this is their second campaign. (Though their first D&D5e/modern D&D experience) For the other three, I am their first DM and this is their first experience with D&D in any incarnation.
My players are all veteran PC gamers. All of them played or play World of Warcraft and League of Legends. I'm not sure how or if this colors their approach to tabletop gaming. Having never played either of those games, and being interested primarily in games of an older style, I haven't much perspective on the issue, and I feel like anything I say must be taken with an old-man-shaking-his-fist grain of salt. (And yes, I am aware that I'm one of the younger bloggers in the OSR at the age of 34, but I am also the oldest in this group, with age differences ranging from 6-11 years younger.)
The game itself seems to be driven by the acquisition of experience points. The players want to get xp. They do things that will net them xp. They do it because they get xp for it, not due to any particular character goal or motivation...aside from, I suppose, the acquisition of personal wealth and power. (You could argue that this goal was a strong part of older editions, as well)
In terms of immersion, this campaign has to be one of my weakest performances as a DM. I feel like I describe the dungeons well enough, but the NPCs have little in the way of personality or flavor, which is something previous gaming groups have lauded in me. In fact, there seems to be very little in the way of RP at the table. The players are in a state of quasi-OOC at all times, and their characters' personalities are essentially just their own real life personalities. I don't know why any of them came to the Keep, nor what their purpose is aside from accumulating treasure and experience. Actually, this isn't 100% true; the party's necromancer has aspirations of rising within the Mage's Guild of the Keep.
While I enjoy the game, I feel like it has none of my usual...pizzazz. I don't think this has anything to do with 5e necessarily, nor the players' background as WoW players. It might have something to do with the fact that all but one session have been played in one of two public venues.
Part of me is curious as to how this game would roll differently (if at all) if we were running, say, Swords & Wizardry or some B/X. Then again, two of the players play in a Cyclopedic D&D game... (albeit a heavily house ruled version)
It's no secret that there are versions of the game I'd rather run, but at the end of the day, I prefer 5e to 3.5 or 4.
...I could get down on some florid-ass 1e, tho. Terraxian forever.