Doyles Super System (in my opinion) is still popular as it was basically the first book of it's kind... the first book to reveal how the pros were playing NLHE (predominately on 'cash tables'). I'd say it's considered a classic.
I've read both SuperSystem 1 & 2 a few times each (I'm a poker book addict... some books I've read 5x+). I've also read over 3 dozen other
poker books (mostly ones that I'd researched in advance to find the best book(s) to read on NLHE) and would have to say that SuperSystem1 doesn't make my Top10 list (<< not even close!!).
Go to the local library and loan it out.... or ask for an inter-library book loan. That way you can read it first before making a purchase (so you won't be disappointed).
I'd suggest reading Phil Gordon's "Little Green Book". It's a good first read on NLHE (well-written...... much different than the "and I got the Five Trey so I can bust 'em" << type of read).
As mentioned above, Harrington On Holdem - Tournament Play Vol.1 (& 2) are excellent books. If I were recommending books to someone... these would be next on the list after Gordon's book ( (s), he has other books too... but read the Little Green Book first ).
Many will swear by SuperSystem.... personally I'm not sure what they've found to be so great about it (at the time I'm sure it was awesome).