The Portuguese language at that time was, naturally, a bit different from all modern varieties:
in terms of (i) vowel sounds (being more open), (ii) stress and prosody (being stress-timed), as well as (iii) a major tendency of putting the "unstressed pronouns" before the verb (in a way that looks like other modern Romance languages, using it after the verb only in some cases) (sentences like "me ajuda" (help me) are common), (iv) the construction of progressive sentences with the gerund (estou andando (I am walking)), it resembles Brazilian dialects.
in terms of (v) consonants, (vi) pronouns and their respective conjugations, it resembles European dialcts, specially those from the north.
And it makes sense, both variaties of the language are daughters of the same previous version, however, all dialects from these varieties had lots of inovations, it is natural. English had many changes from Shakespeare's time to modern days, such as the Great Vowel Shift, the general lost of thou, thee, thy, thine and the second person singular conjugation etc. It is also worth noticing that Camões and Shakespear lived at the same time and used a very poetic and refined vocabulary and stuff.
So, knowing that, I add that no, it is not a good text when you start learning. I guess you could study it as one studies The Eneid for instance, but you will have to know some Latin before to do that, or Antient Greek for the Odyssey etc.
Here you have the first edition of "The Lusiad", the translation of "Os Lusíadas" in English.
Versions in Portuguese are really easy to find online and in physical copies!