I'd like to visit Estonia and the rest of the Baltic countries in the summer. How are the crowds? Will it be like say, Italy?
Tallinn can be very busy (but nothing compared to Rome or Florence) especially when there are several cruise ships in port (Dates and numbers can be found on line). You could time your visit to Tallinn to miss the worst of the cruise ship dates. There would be no crowds in the rest of Estonia at any time.
Riga and especially Tallinn get cruise ships, so on days with multiple ships in port, they could get crowded. The rest of the Baltics don't get cruise ships.
I visited Tallinn and Riga during the summer of 2018 with day trips into the surrounding areas. The old town of Tallinn was oppressively crowded during the day when cruise ships were in port but absolutely lovely in the evenings. I walked Toompea Hill in the early evening and had it virtually to myself. I was in Riga during the every-5-year Latvian Song and Dance Festival. Even with the festival, I did not feel like the city was terribly crowded. The surrounding towns and nature areas for both cities were not crowded at all.
My first trip to Tallinn was in mid-Sept and it was lovely--still nice weather but not crowded. I went this year in late April-early May and it was also pleasant as far as people go, but rather chilly, a bit rainy, and even snowed.
We visited Tallinn in June and it was pretty crowded. As well as the rest of the Baltic ports, especially St.Petersburg. If you would like to avoid crowds, May and end of September are better options.
There are quite a few cruise ships in the Baltic during summer. In most places, they will leave port at 6 pm, so after that, it will be a little more peaceful. If you are flexible with your dates, my suggestion will also be to go a little later in the summer. And check how many ships wil be there with you... it can get crazy!
I just got back from Tallinn on Oct. 9th, 2019. Excluding the weekends during the day in Old Town, I didn't think it was very busy anywhere in Old Town. As someone mentioned-the rest of Estonia is almost devoid of people. There were a few sunny days, but most of the time it was overcast and it rained quite a lot, but most of the time it didn't last very long, either. I found Tallinn to be easy to get around, almost everyone speaks very good English, it is very clean, and I felt very safe. (It is one of those places where they often leave the baby carriage outside a restaurant, unattended.) The Old Town also has free wifi throughout the city. I also went to Finland, Latvia, and St. Petersburg, but I felt Tallinn was the cleanest and safest. I didn't find any of the Baltic Countries or Finland, or Russia to be too terribly crowded, especially if you are comparing them to any town in Italy. Actually, no comparison. I have been to Italy in the summer (forget about it) and in the Fall (okay, but still crowded) and I feel the most crowded day in any of the Baltics, Finland, or Russia, was still less crowded than the lightest day in the Fall when I was in Italy.
How are the crowds? Will it be like say, Italy?
No. Crowds won't be anything like Italy - not even close. It's like a different planet.
As others have indicated, Tallinn does indeed get cruise ship crowds, so during cruise ship time (mid day hours), during the peak summer season, the old town will be crowded, sometimes quite crowded in places. But even then, it's nothing like the crush of humanity that you would experience in popular Italian tourist destinations. Even at it's worst, Tallinn is just "busy" not heartbreaking. When the cruise ships are gone, the place is lovely, like a traveler's dream.
Elsewhere across the Baltics, Riga gets some cruise ships too, but it's such a large city that it seems to absorb that without becoming overwhelmed. Riga never felt very crowded to us (midsummer, peak season).
Besides Tallinn and Riga, you would have to work hard (and really stretch the definition of the word) to find anything that you could call a "crowd". We traveled through these countries for almost 3 weeks at the height of summer tourism season, and until we arrived in Tallinn (the last stop of our trip), we never heard English being spoken (except in reply to us asking questions), and we never saw another American (as best I could tell - I was on the lookout) the entire time we were there. It was...blissful.
Tallinn was crowded in October.