There are a few minor differences, but they're the sort of things that any Italian edition would have footnoted for native readers. However, I would say that the difference between Medieval Italian and Modern Italian is a bit less than the difference between Shakespearean English and Modern English. A far greater gap exists between Medieval German or French and their modern equivalents, and even the English of Chaucer is probably farther from the modern idiom than the Italian of Dante.

And frankly, I don't understand why someone would read something like Gerusalemme Liberata or Orlando Furioso in translation if that same person plans on reading anything in Italian at all - all poetry loses an incredible amount in translation. For example, the beginning of Tasso's epic starts as follows:

Canto l'arme pietose e 'l capitano
che 'l gran Sepolcro liberò di Cristo.
Molto egli oprò co 'l senno e con la mano,
molto soffrì nel glorioso acquisto;
e in van l'Inferno vi s'oppose, e in vano
s'armò d'Asia e di Libia il popol misto.
Il Ciel gli diè favore, e sotto a i santi
Segni ridusse i suoi compagni erranti.

So what is hard about that? I am looking at the eight lines and see almost exclusively modern Italian words. A few final vowels have dropped, as is typical in Italian poetry (popolo > popol, vano > van) and operare contracted a bit for the same reason, as did a couple of places where a full definite article would normally be found. All of those characteristics could appear in any modern Italian poetry, however.

In fact, there is only one irregularity: diè, which in Modern Italian would be diedero. This is a major contraction, but once again, it's pretty easy to determine from the context if you know your conjugations.

At the level of syntax Tasso has thrown in some Latinization, saying Sepolcro liberò di Cristo instead of Sepolcro di Cristo liberò, though that's probably to keep the rhyme scheme as much as for any other reason.