We recently booked a land/sea package. Originally I booked our trip as a packaged. But after much research figured it is cheaper to book everything separately. First, the land/sea package does not give you any hotel discounts. I was able to find on mousesavers a coupon code for $100 off a night at a deluxe resort. So, we ended up saving $400 for the room. As a result, we added two more nights to our stay. Also, the package you are given the Ultimate Park Hopper pass which gives you access to all the parks plus water parks, disneyquest, etc... However these park passes are only good for the length of your stay. We found in our case that it would be a waste because the first day that we fly we will not be able to use our passes because we don't get in until 11 pm at night. So, day 1 is wasted even though we paid for it. Second, in 4 days I doubt we'll see everything. We decided to buy park hopper passes which gives us passes to the 4 main parks which is probably all we'll have time for. Also, the passes do not expire so, if you miss a day then, you can apply your credit to your next purchase. Also, disneyclub members can buy the passes at a discount. Finally, the transportation fee included in the package is very expensive. You can rent a car for much cheaper than Disney charges for 4 people.
Good Luck with your decision.