I visit Tallinn every 3-6 months and love Old Town but one trip was during cruise season. A strong bit of advice, go there directly, not on a cruise ship because of two main reasons:
1 Ships only allow a few hours ashore
2 When several ships in in port, it get extremely crowded.
Fall winter or spring is very different and far more interesting. The city of Tallinn is pretty normal and not the attraction but the walled city Old Town is a delight when not overrun with tourists. All other times is is slow paced, friendly, and engaging. Walking can be a challenge with the wrong shoes, the cobble stone streets are frequent causes of falls so wear something that has some protection for the soles of the feet like leather shoes, light walking shoes made for smooth pavement will cause burses on the feet, and look at your feet to make sure you are landing on where you intended. It is is a lively living community there, when not overrun by tourists, so pop into any shop, pub or cafe that is not crowded and you will make new friends, but in busy season no one has time to talk or relaxed enough to engage. Of the Baltic region, it is only second to St Petersburg as fun and interesting destinations.
Either be good at map reading or use a smart phone to identify where you are and where want to go because the narrow, winding lanes can really disorient you so you can't tell what direction you are heading. All the cafes and restaurants or pub fare seems reasonable or about 1/2 of the cost in Finland or Sweden. I usually stay in single bed hostels rooms for $12-20 a night but the last time stayed in a hotel further away that was very nice for $40 but it was a pretty good walk to get to Old Town, over a pretty steep hill. Climbing over the hill with lush parks was really nice, west of Old Town Nice hotels in Old Town, are USD65-190. During peak season they can be a lot more and it is more like DisneyLand than an historical destination for relaxed exploration it is for 3 seasons.
Overall off season prices are low, lower than anywhere in the Baltic except St Petersburg, A bonus is Tallinn to St Petersburg by bus or train then bus is low cost and easy so spending a week in Tallinn and 1-2 weeks in St Petersburg.
