If its not a secret deal between Russia and Iran to licence produce a somewhat different T-90SM as Karrar in Iran, then Iranian designers basically took the design philosophy of the T-90SM to upgrade the T-72S design they already had.
From my point of view this is great as the turret shape of the T-90SM is really a very good design, it allows a large degree in azimuth to be covered by the turret armor. This means it can hunt for targets at a wider are without exposing itself.
So this modification of the T-72 design is almost the best you can get. The turret bustle allows additional armour to be carried outside the crew compartment as opposed to the original T-72 and basic T-90 design.
Now to possible downsides:
The tank gets heavier by this changes. The ~800HP engine of the T-72S would make the tank quite under powered for today's standards. Iran possibly can still import those engines for the Karrar but I don't know wither Russia agrees to sell the 1000Hp and 1000+HP engines of the T-90 family. An Iranian tank engine was not yet shown.
The gun is still the Soviet 125mm but with some fancy looking changes. If the autoloader has not been changes there should still be limitations for longer rod APFSDS rounds. This would basically locks its main gun firepower to that of the T-72S. The Russian T-90SM has the necessary changes for the autoloader as far as i know.
Russians have decades of experience in armor due to the huge efforts by the Soviets. It remains to be seen if ERA and amour of the Karrar are up to those of the T-90SM. At least the sideskirt ERA seems to be a mock-up or not installed yet.
I see no Independent sight for the commander.
No muzzle reference system on the Karrar as on the T-90SM. Also the APU and infantry communication port is missing.
Even if all this lacks remain true its still a great and economical design. It could be a bait for the Russians to say "look we built almost something like your T-90SM, come on let us licence produce it here".