This is a very popular museum overlooking the lake in Cleveland. We were a bit annoyed when we had to wait in line for 40 minutes to get our tickets. If you plan to go on a weekend, you might want to order the tickets through Ticketstar ahead of time to avoid the wait.
Once we got inside the museum, it did not seem crowded. There were hundreds of interesting exhibits to explore. You could easily spend most of a day at the museum. Our kids loved it. The omnimax theater was also very nice.