First of all, there are two key points in my opinion that can help convince players to continue to play an online manager game, despite the abundance of other entertainment options in the modern world.
The first is to make it a relatively fast paced game so that the player always has something to do or look forward to. Hence why I mentioned three league games per week and shorter league seasons. I was put off signing up to Charazay for example because of 17 week seasons, when they could've fit their league schedule into 11 week seasons if they used the three-league-game week format and had the off-season only last a week. BuzzerBeater just about gets away with 14 week seasons as it is...
The second for me at least is to promote the site's forums and try to make them as lively as possible to give players an extra incentive to log in regularly. This ties back into giving the player something to do, and can also give the game something that an action sports game like NBA 2K can't; a big community that the player can be part of.
One of BuzzerBeater's strengths in my opinion is it's game engine, so any new basketball manager can and should aim to refine what works in BB rather than try to re-invent the wheel. On the numbers side of things, I'd like to see fast-break opportunities via a speed attribute, and a salary system, be it via a carefully constructed formula, or a contract and negotiation system if it can be pulled off, that's balanced in a way so that no one tactic is dominant like LI was in the pre-GDP era.
On the visual side of things, implementing a community assisted commentary line pool like there is in BatTrick could help make the games seem more interesting, and I would also look to improve the accessibility of the in-game chat, my idea being a global chat room as well as a national one, that can be accessed from anywhere on the site and not just on live/replayed game screens. This goes back to that big community I referred to earlier.
Training wise, I propose a system where you can select one skill for the team as a whole to train each week (or more depending on how often you want training to update), whilst also having a limited number of slots to give your promising individual players an extra training session each week.
The alternate, more complex system is to have just the slots for off-day training and instead base team skill pops on where each player plays and what actions they take. Would have to be balanced out by a fatigue system so that smaller teams don't have too big an advantage in regards to training prospects by giving them playing time. In fact, maybe implement fatigue anyway, replacing game shape.
I like the draft and potential systems in BB, though I would have scouting the draft revolve around hiring scouting staff who can then be asked to look at prospects, with the accuracy of their findings depending on skill. Not sure what else to add to this at the moment, but the general idea is to take some level of inspiration from this game, but use the new platform to implement game improvements and features that BB can't have, at least not without a major overhaul...