I just started a game in novice, and so far it seems fairly easy. I'm about to take the 3rd (southern) part of Drassen on the morning of the 2nd day without much trouble at all. I started in novice because I kept reading about how hard the game is. So I'm just wondering if the difficulty is going to ramp up a lot after Drassen? If not then I will probably start a new game at experienced because I want somewhat of a challenge.

Thanks

Novice by default has quite a few bonuses for the user, including a bit lower equipment for the enemies. The difficulty will increase a bit later on, mostly due to the enemy having access to mortars, laws and grenades, but I'm not sure if it will be a challenge or not.
As for the "hard game" part, it does depend on what you consider a normal game. I'd suggest starting on experienced (normal equivalent) for all games btw, and if that proves too hard, move to novice (or easy).
Also, once you do a couple of playthroughs of 1.12, go grab 1.13 and tailor it to your specific needs.
Enjoy the game, it's an excellent one.

What JMich said above. I would only add that, yes the game does get more difficult(in leaps and bounds) the farther you progress on any difficulty. Us vets won't touch 'Novice' because we have likely been playing the game since 1998 or so but if this is your very first play through then playing on novice is a good move only because there is SO MUCH to this game, from knowing which mercs work best together, how to get vehicles and fuel, the best tactics for taking out SAM sites, the HtH matches in San Mona, training militia, etc.

And I have not even mentioned the sci-fi aspects, IMP creation, etc.

That is one thing I'm curious about, what are the sci-fi aspects? What exactly does it change besides adding those weird creatures and a few laser guns?

In vanilla JA2 IIRC Sci-fi mode only introduces the 'Crepitus' and the robot merc. I am not positive which versions of 1.13 change this or the extent of their changes(I am currently playing an older "STOMP" version). A lot of us used to wonder aloud why the Bloodcats and regen-syringes /boosters and such still existed in "Realistic" mode..