Ashtanga is good if you don't mind repetitive motion since the postures never change. It's not like Hatha styles where every tape can be a totally different set of postures. Generally speaking, Ashtanga is very physically demanding, should really be done under supervision, and can easily lead to injuries if you are not aware of how to properly protect yourself and modify postures for your skill level. Also, the pace of an Ashtanga class may be faster than what you are used to with a regular hatha class.
I have not seen any beginer Ashtanga tapes, so I do not know how good they are. A full primary series Ashtang tape can be a bit overwhelming and intimidating.
Regarding some misinformation:
Ashtanga yoga is not power yoga but is a subset of the umbrella Hatha. Power yoga (or Vinyassa Yoga) is a faster, flow-ey type of yoga, but does not use the strict posture sequence of Ashtanga.
I personally find Ashtanga much more relaxing than hatha, becasue it suits my personality. Iyengar drives me crazy
You may find that Ashtanga stresses you out. There are so many flavors of hatha, I'm sure you can find one that works for you.