Man, this question has been done to death, so much here as on every other mj forum on the Net in this and every other parallel universe.
Can't we just have it in a FAQ, or pinned or something?
Here's the main things I'd include:
1) There's nothing basically wrong with Nirvana, and they are not "that cheap", simply entry level. Other breeders like KC Brains, Mandala, Sativa Seedbank, etc. charge about the same.
2) It'a a bit daft to ask about Nirvana seeds in general, a look at their catalogue will show 5 pages or so of strains. It would be impossible to generalise totally over so many different seed types.
3) They are on the whole quite good for beginners, especially rank beginners who are error-prone. Some of the expensive seeds can be quite difficult to grow (and some very easy

), at least here the investment is small if something goes wrong. Remember that there is a surprising number of people trying to grow who have never even grown as much as a (non-mj) pot plant before. Bound to make some silly mistakes then.
4) Nirvana copy a lot of other breeders work. This can make them morally questionable in the eyes of some people.
5) However, Nirvana also have some F1 strains of their own. These can be quite good, and some of them are very popular.
6) In general, Nirvana indicas are good and easy. More of a question mark over their sativas, at least for beginner ease.
6) Be careful when you hear newbs trashing Nirvana (or anything else). The cause is very often their own (sometimes quite basic) mistakes.
7) There is a lot better stuff than Nirvana. Then again there is a lot worse. Probably the Ford Cortina (practical / basic) of seedbanks.
8) If you are asking this question, chances are it's more important to pay attention to basic growing principles. If you are on a tight budget, though, a traawl through Nirvana's (and other similar cheap breeders) catalogues cab reveal some gems.
If the fancy takes you, try them!
Not much more you can say, really, IMHO.