Some observations after a few hours of playing (mostly 15m Q + 25% races):
1) I haven't played the previous versions, so I have no idea how much the AI has improved, but it's still not great. Sometimes as if it just ignored you completely (other drivers turn into you in the middle of a straight etc.). And of course, once they've crashed into you, they do not start braking until you both DNF. Although I must admit it's refreshing to see them race much more aggressively than in the original game.
2) Out of the tracks I've tried so far, there has been one where pitstops don't work at all. It's Brands Hatch (a.k.a. Zandvoort in this mod). The pit crew doesn't come out and just lets you through. You don't even have the pit limiter on. So yeah, no way to finish that unless you switch to 5-lap races, which are pathetic.
3) As has already been said, the flips are extremely annoying. There seems to be no logic to when and where they happen. It's also not always on a kerb, but at times even at a completely random place. And then some dangerously looking kerbs are totally fine, so what the heck? If this issue has to do with the 18-inch tyres, then (as great as they look) we might not need them.
4) I've already asked for the difficulty to be increased and thank you for your reply. If the only way to do it is to downgrade the player's car, then so be it. When I say that the "hardcore" difficulty is way too easy, I mean "fastest lap in a Williams" kind of easy. I will say, that the dificulties were pretty even on all tracks I've tried so far, which is unusual for such mod. Good job.
5) And finally, I definitely second the people who asked for the dynamic racing line to be imported where it's missing (e.g. Valencia). If it really is possible (as you admit), then it should definitely be there. Some people need it and shouldn't everyone be able to enjoy this mod properly? It's been brought up a couple times already, so it's clearly not something to dismiss. In fact, it should be one of the priorities for forthcoming updates along with the unfunctional penalty system.
Overall, definitely the best looking season mod for F1 2014 I've seen (the liveries, the wheel covers, current sponsors around the track etc. - all terrific!), but at this point pretty much the least enjoyable to play. The visuals are perfect as they are, not everything needs to be super realistic (people asking for helmets and stuff like that - jeez, really not important!), there are many other things that should be focused on in terms of playability. Looking forward to future improvements.