The thing with IS's final dungeon is that based on a dialogue choice halfway through, the remainder of the dungeon will either be short, medium, or long. I played the import and overthought it, so I ended up picking the longest and most tiresome path.
Another difference between IS and EP is that EP only gives one individual contact skill per character and the focus is more on group contacts; what's cool about that is that if you pick Katsuya before Ulala, the contact is different than if you pick Ulala before Katsuya. Another difference also is in how rumors are handled. With IS, you could spread the "cheap/bad, mediocre, or expensive/strong" equipments, but with EP some rumors change the TYPE of equipment a potential store may have (i.e. special weapons vs. special armor.)
The IS import took me 80 hours or so to complete (most people at the MegaTen boards I used to mod took about 50). I maxed out EP's clock and I assume I sunk 110 hours in. I waited months in between both games, so I didn't get burnt out.