I personally think Sealion is a trap. Its so enticing, and even more so that its just about a guaranteed win. The problem is that to pull it off, Germany has to invest a massive amount of resources, and it spends precious time. Even if you are successfull, and you conquer the UK G3, you have invested in transports and a fleet which will be sunk by the US, and you have yeilded the initiative on the Russian front. Unless you attack the Russians G2 with everything you have, you really have no chance of getting past the Ukrane. The Russians just have too many infantry. Combine that with the fact that the Germans will barely break even once their fleet is sunk by the US, and the Axis is in decline. The Germans are in a bad spot.
Moreover, an intelligent British player will not waste money defending the Isle beyond the cost effective point. Because Sealion is obvious G1, the British can adapt their play so as to fight the Italians with great success in Africa. I have seen the Brits fight the Italians, while their capital falls, they have the US reclaim it US5, and then the allies are OK, and the Axis is in trouble.