I go back and forth. I'm a pretty big fan of the Lego games in general- they are ones that my wife and I consistently play together- and Dimensions is no exception.
I think that there were two key appeals for Dimensions:
The physical bricks and minifigs. Lots of neat parts and some exclusive minifigs. Doesn't hurt that they would see discounts more in line with video game sales as opposed to (seemingly less frequent) Lego sales.
Franchises getting a (Lego) gaming treatment that otherwise would not. Doctor Who, Gremlins, Goonies, E.T., etc,
Point 1 applies to Lego hobbyists far more so than a more casual gamer. One reason my wife stopped enjoying the game as much was that there was simply more setup involved to actually play (and with as two-year-old running around the house, we need to be sure to put everything away when we're done). Having the tethered portal (as opposed to wireless) didn't help things either: couch co-op suddenly becomes more complex and cumbersome.
Point 2 applies to gamers more in general, but can sometimes be a hard sell for Lego Games' majority demographic.
While I'm an ideal demographic (both points 1 and 2 apply to me), I'm not the target demographic per se.
I don't think we'll see Dimensions continue on in its current form (which is a shame for me, since I do love the series). That said, don't be surprised when something similar but different shows up down the road. I recall reading how there were three approaches Lego was going to take with the digital space that eventually became Fusions, Dimensions, and Worlds. Fusions was an awesome idea that couldn't be executed to its full potential, Dimensions was an awesome idea that is necessarily driven by demand in two disparate markets (physical and digital), and Worlds is still in its infancy.
Both Lego bricks and Lego games are incredibly successful products, and a closer alignment of the two is not surprising. Will be interesting to see where it goes next.