rules difference between Drakensang and RoA
 

So, let's say once I finish this game, and hopefully finally understand all the rules, if I decide out of curiosity to play the RoA trilogy, how different would the rules be? Are things like attacks, parries, talent checks, etc. basically the same? Spells, classes, etc? Is it radically different or very similar to Drakensang?

Attribute and skill/spell checks are essentially the same. The available skills will be different, and the leveling and character generation will be very different.

And there will be a lot of micromanagement.

I have yet to start Drakensang. Does it have skill increase difficulty rolls as ROA did, or it has a simple point buy like those mobile text-based DSA RPGs or their browser-based cousin?

No luck involved when leveling. You buy the points for skills, attributes, vitality points etc.

Point buy.