BlitzMax is crippled compared to C#, in it's memory leak prone garbage collection technique
I haven't seen too many bug reports of memory leaks. Those that are often turn out not to be a leak more a misunderstanding how GC runs.
I mean programming the DX10 API, not some crappy 2D DX7 commands.
Oh.. although you didn't cite that as a disadvantage? I am a bit surprised nobody has created a DX8/DX9/DX10 interface though. I wonder if there's a market for it?