If you really just want to play SA2B with other SRB2 characters, then you might as well get it. I just find some things a little odd.
NOTES
/ Aquatic Mine and Crazy Gadget are absent, oddly
/ A lot of stages seem to be cut short.
/ Final Rush notably is completely different than how it is in SA2B. I would be fine with having levels be reimagined, but City Escape looks to be a close replica...
/ Death Chamber and Meteor Herd are a bit on the small side
/ No Dark Story. (Yet.)
If you want my idea on how to make Aquatic Mine, maybe have three copies of the same stage with the difference being how high the water level is, and include teleporters on the switches.