Over the last year or so, I've had the pleasure of looking at about half a dozen extended BASICs for the C64. Without question this is the most interesting. This package is certainly not the most sophisticated, although it's pretty close to it, but it's the first which is effectively an emulator.
You can convert your C64 into a C16. You might question the value of this, but even if you don't want to use C16 listings, the version 3.5 BASIC it offers is a great deal better than the resident version 2. To test the compatibility of the package, I tried entering programs on the CI6, saving them to disc and reloading them into my C64. They worked every time although there are one or two areas where the package doesn't behave as version 3.5 BASIC.
I won't attempt to describe version 3.5 BASIC in detail. It offers commands for hi-res graphics in two modes, structured programming, toolkit commands, sound and a variety of BASIC enhancements. To offer full use of the sprites on the 64, commands not covered by version 3.5 BASIC are provided but .that can't be a bad thing.
The package NOV ALOADs and on running you discover that you have only 26K free. If you use hi-resolution graphics, you lose another 12K. I found this peculiar since it's quite simple to use the RAM behind the kernel ROM for graphics. Overall this is a first class package which represents excellent value for money.