Hey Arora,
First off, congratulations on a 670, which is no easy feat...I think it's important for all of us with significantly-above-700 aspirations to remember that scoring in the 84th percentile on the GMAT is impressive - that's better than 84% of an already-successful group! The average person doesn't sit for a graduate admissions test...to even sit for it signifies that you're significantly above average academically, and to score that high in a range of such people is something that you should be able to take some pride in!
Now, that said...I know you're interested in and capable of an even-higher score, so let's set sights even higher! A few thoughts:
1) Be confident - you admittedly struggled in spots, felt some real stress, and still came out of it with a strong score. 670 is your baseline now, which should provide you with the confidence to overcome that stress and pressure next time out. One of my most devastating life experiences was when I was on pace to qualify for the Boston Marathon for the first 20 miles of a race and then crashed and burned the last 6...until a day or two later when I realized that I was incredibly close to that goal. I ran that pace for 20 miles, and could better train and strategize to keep it up for 6 measly miles more. Six weeks later I did, mainly because of the confidence that that first "failure" gave me.
2) Another confidence-builder is that hopefully you recognize now that there's no great way to gauge your difficulty levels on the test, so don't waste energy on it. If you're waiting anxiously for one of the "hard" problem types (Boldfaced CR, Permutations/Combinations, etc.), it may not come, but that doesn't mean you're not doing well...you may just have been hit with similarly-difficult problems in other genres. One of my favorite examples of it is this one:
https://blog.veritasprep.com/2009/03/gma ... -week.html. This student was so convinced that she bombed the quant that she literally couldn't function during the verbal...and ended up over 90th percentile on the quant with an awful verbal score that rendered all of her great work on the quant moot. Stay upbeat and you'll probably surprise yourself with how well you're actually doing.
3) If you can get your hands on our Critical Reasoning 2 book (available on Amazon and I think now on the iPad and Kindle if I'm not mistaken), it goes through a lot of strategy on some of the "new difficulty" questions - "best completes the passage"; "which would be most useful to evaluate"; "assumption", etc. David@Veritasprep and I can't get enough of talking about those kinds of questions, so post those on here, too, and we'll chime in.
4) I've heard a lot of, as you said, the quant section focusing more on algebra and number properties and less on geometry than in prior years, so I think you're onto something. Keep in mind, also, that most geometry questions become algebra questions after 1-2 steps (e.g. Pythagorean Theorem, which is really all about the a^2 + b^2 = c^2 algebra once you've recognized the right triangle), so you'll never regret working on your algebra abilities!
Selfishly, I think we're all happy to have you on the boards for a little bit longer, so hopefully your first misstep will not only help to provide you with more confidence to maximize your score the next time out, but will also provide the rest of the community here with great dialogue and insight for everyone else's upcoming tests!