Re: should i even bother with sci fi
There is a lot more to science fiction than just the classics. YOu may be choosing books that are too hyped up, not that they aren't oftentime brilliant, but if you are new to sci-fi, you should start slowly and work your way up. Ender's GAme by osc is a good beginners scifi book (although it too is a classic now). David Weber's Honor series is excellent if you like military sf in space. You probably will enjoy the Foundation series (I know, I know, classics again) if you liked the Robots.
Science fiction isn't all robots and space either. You might find yourself a fan of steampunk, or time-travel, or alternate history (World War Z is excellent).
IF it is disappointing you to buy books you later get bored with, consider Baen.com for free sdcience fiction downloads. It's a great way to figure out what exactly you like, so you can make better purchases in the future.