Incidentally, the Nirvana WW is an F2 Widow.
F2 seed yields a lot more varied phenotypes than F1 generation.
WW is a sativa dominant strain, but you will find some plants with phenotypes leaning on the sativa side and others leaning on the indica side.
That's not to say they're bad necessarily... sometimes a freak phenotype F2 kept as a mother can be quite wonderful. It's probably better to go for F1 or stable seed if you are not growing from clones though

If you want to try something closer to "the real thing", pick up Black Widow from Mr Nice seed bank. It's totally stable and would be more vigourous than most F2s (and more uniform, which is essential if growing from seed, really)...
I grow freak Nirvana F2 WWs from cuttings btw
But i'd love to try Mr Nice's too

edit - when i say freak, i mean freakishly good, obviously, har!!!