Seconding much of what lawkeeper stated, I don't find as much game play problems with the Tangiers strait as the Dover and Irish Straits (playing SP only for this and all following observations). Spain has not, in more than 6 games (no, I was not playing as Spain) taken over North Africa. My critique centers on:
1. England's only hope is to crush France early. Admittedly, the strait helps in this if you are playing as England, but then you end up battling Burgundy and the French minors, rather than have a rivalry with a powerful France. Not quite as satisfying.
2. Scotland has, in all 6 games, taken over every Irish province but Meath. I guess this is better than Spain and Genoa having Irish provinces, but nonetheless ... (no, I was not playing as Scotland either).
3. The English AI, even if it has a large fleet, is oblivious to the threat of French troops in or near Calais. The fleet sits at harbor rather than block the French advance. Even after the troops have marched over the straits, the English AI makes no attempt to block additional reinforcements. If you play SP as France, you end up as the hegemon in Europe before 1500. Then it simply becomes a game of picking up German minors until you lose interest and start colonizing.
4. Some might criticize this change for even further devaluing the already almost useless transports, but since I never ever build them I can't use this as a valid criticism. (In fact, I go so far as to disband any transports I gain as a result of random events or annexations - why pay maintenance for them?).
Proposed solutions are one of two things; either get rid of the Irish and Dover straits, OR make the transit times on these straits be very high to mimic how long it would take to assemble a flotilla of barges and fishing boats. I know that the latter is possible, it was just never implemented in the finished game (i.e., making transit times different for different provinces). A well designed model along these lines would alleviate a few concerns, including not only allowing England (for example) to rapidly redeploy a fleet when a large force of French are beginning their slow march across the water but also better model the differences in marching times across the huge Asian provinces versus the smaller European ones and give transit penalties for crossing mountains (with smaller penalties for marshes and forests). If this could be implemented, I'd like to see EU programmers get rid of all straits and use this "extended transit time" model.
My two concerns are whether or not the English AI would, even with the increased transit times across the Dover strait, respond to the threat in time to at least put up a battle 9 times out of 10, and whether or not Scotland can be inhibited from crossing the Irish straits every single game. I've got no problem with the variability that the game allows, I just balk when I see the ahistoric options occur so frequently. Maybe Scotland, if all went well and England was engaged elsewhere, would have grown into a rival to England, but that shouldn't happen every game. Nor should either France or England be subdued every game; most games, they should both survive and prosper in spite of their proximity.