I find webOS to have the current best multitasking, cards that are opened are running apps and they will and you can open as many apps as you want (until you run out of RAM, then you get the too many cards error), With android, multiple apps can run but the OS will randomly decide to close them (but their icon will still be in the recent apps list so you never truly know hoe many apps are running, and you run into issues when you go into another program for a while then head back to the browser only to find out that it closed it's self but saved the state and now every tab needs to reload.
Is it too much to ask for? Just have a touch friendly way of managing running apps but handle them the way a desktop OS does, eg in windows you now when a application is running and the OS will not randomly close them because you were in another active app for a while.
If blackberry wants to be successful their new Os better support android apps and it better have good multitasking in way where apps don't go into a sleep mode when minimized and where they don't save their state and close them self completely because you have not checked on them in the last 20 minutes.
Other than that, apps are the most important aspect. look as how webOS failed even though it has a better UI and far better multitasking and was more screen space efficient. The main issue was there were not enough apps and no one buys a computer smartphone and only uses what it comes with (how many of you bought a windows based PC and never installed any software.
How many of you would use windows if it has no additional apps and only allowed you to use what comes with the fresh install? The answer should be obvious and shows that the goal of a user choosing an OS is not the OS it's self but what they can do with it and run with it.