I agree that BL is a visual feast, and amazing that Kubrick (along with NASA) developed a camera so sensitive that it could film scenes lit with only candle light. And I agree that it's very long, and very slow. If you are in the mood for something that moves along and is very plot driven, then BL is going to be rough going.
But if you know that going in and can sort of 'relax into it', then it's a pretty interesting film. At least that's true for me. As is often the case, Kubrick is more interested in power structures, in-group vs. out-group dynamics and an overall sociological perspective. For me, this really lets one get a feel for what it was like to live back in those times (ie, not good).
Some things that are great about the movie don't become obvious until a 2nd or 3rd viewing. For example, we've all heard about the "unreliable narrator", which usually happens when the story is being told by the first person (ie, a movie like Goodfellas). And normally 3rd person narration is for the more 'objective' viewpoint. In BL Kubrick is very sly about making the narrator English and of course Barry is Irish. At the time the English outright loathed the Irish. So throughout the whole film you have this English narrator just dumping on Barry and basically talking shit about him the whole time.
One other thing I didn't get at first was just how uncouth and embarrasing it was (back then) to gatecrash into the nobility. The nobles were the nobles and everyone else was riffraff and just the sheer audacity of Barry trying to become a nobleman was preposterous. As an American I was sort of blind to it, because over here there's not a stigma against 'making it' and becoming better off.
TLDR - if you ever are in a langorous mood in the future, BL might be worth another go.