I've only played each track a little, so this is based on a lot of first impressions, but here goes.
Sepang is a fun, fast track. There's a lot of rolling in fifth and sixth gear. The backside is a tricky rhythm section with a lot of tough choices between fourth and fifth gear. Many of the turns are short, and the straights are in-between distances, which is a bit unforgiving and this track is tough on cars. There's a lot of hope for high rolls, then burning gas points to get into third gear because you came up short. On the other hand, the track seems to spread cars out, so there were few collisons.
Your rolling in the back section will make or break you on this track. You can make up a lot of time, or you can lose it. The races are spectacular, because it takes guts to win here, which means a lot of people are praying not to wreck as they come around the end of the track.
The hairpin at the end might be more realistically rendered as a longer 2-stop turn, because taking it at 5/6 is common and 6/6 isn't that rare. But, who wants a slow 2-stop turn heading into the home stretch? The choice to go one-stop is more in keeping with the feel of the track and is more exciting.
This is one of the most fun tracks I've played. It's like Watkins' Glen's devlish cousin. You'll either be elated or crushed when your race ends, but you'll be excited. Sepang might be my new favorite course. I wouldn't conclude a season with it because there are better skill-tracks, but I'd certainly include it in every season, (I play almost exclusively in 6 to 13-race seasons) and it's a terrific track for beer-and-pretzels game nights.
Difficulty for first time players: moderately easy to moderately tough (you can just grab a gear and throw here much of the time without a lot of space counting and thinking and still be competitive if your luck is good. It's a lousy track for someone's first point-built car, though.)
Luck factor: moderately high
Overall: 9/10 A great track. Great.
It's a good thing Sepang is so awesome because Zhuhai is not. There are only two 1-stop turns on the track, and one of them is an awfully small target. There are no straights that end in one-stops on both ends, so you're always off to a slow start in a straight, or you're gearing way down at the end. Zhuhai is really slow. The straights and turns tend to be in-between lengths, so this is another track that's hard on cars. Four of the six two-stop turns are u-shaped, so getting bumped to a really ugly inside track happens a lot.
In this track's favor, there's a lot of opportunity to make up time (which translates to lots of opportunity to lose it too), so you can catch up to someone who storms off to an early lead, or come back from a bad start.
Fortunately, the last two straights and final turn of the track are very fast, so the finishes are exciting, but it feels like a chore getting to them.
In all, I don't play F. Dé to roll in fourth gear all day, so I have to give this track a resounding "meh." There are better skill tracks for tournament play (I'm a fan of Kyalami Circuit) and there are much, much, much more exciting tracks for beer-and-pretzels play.
I'd rather play Zhuhai than Monaco (which I really don't care for) but that's about it.
Difficulty for first-time players: Moderate. (It's not that hard. It's just boring. Also not a good track for a first point-build.)
Luck factor: moderate
Overall: 4/10 I'd play it again, but it wouldn't be my first choice, and I'd avoid three-lap races on it.
Value for the pair: I think Sepang is worth the price of the pair. I highly recommend this set for it alone, especially if you have a few tracks already. If you're shopping for your first expansion, I'd recommend Watkins' Glen/Silverstone or Zandvoort 2/Spa-Francorchamps instead, because in those sets, both sides are fun to play (though none are Sepang good.)