How to tell whether invitation to special issue of a journal is worth being accepted? I have been invited to participate to a special issue of Entropy for some work that I have done in statistical physics. 

I received from other journals many such invitations which looked like spam,  and I wonder whether I should take this one more seriously, or consider it somehow a good one. 

What are the criteria to tell whether the special issue is 'prestigious' enough, besides Impact Factor and names of guest editors?
First things first, Entropy is an MDPI journal. MDPI is a rather controversial publisher - see the "Controversies section of its Wikipedia page - and while I make no judgment on whether it's a predatory publisher, it's preferable to know the facts so you can make an educated decision on whether to publish with them.

If you conclude that it's worth publishing with them, then factors to consider are:


Do you have anything relevant to contribute to the special issue?
Do you know who the editors are? Are they authorities in your field?
How good is the journal? Have you read/cited papers published in it? If not, you can still look at the papers in its current issues and draw your own conclusions about its quality.
Which databases are the journal indexed in? This is usually a concern, but since you mention "impact factor", that means the journal is indexed by the Science Citation Index, and that's the index to be concerned about. If the journal is indexed there every other index doesn't really matter.
How much is the article processing charge, and can you afford to pay it? MDPI is an open access publisher, so you can only publish OA with them, which usually means there's an APC. It's possible they're offering you free OA (this is especially likely if you're an invited submission, similar to how invited conference speakers often have the conference attendance fee waived). Otherwise they might simply be letting you know that you might be interested in this special issue, in which case you'll probably need to pay the APC.


But in the end the final decision is up to you. If you submit, acceptance is not guaranteed, although I'll venture that your chances are relatively good. If yours is an invited submission, then you might get to list that prominently on your CV; even if not, it's still +1 to your publication count. But preparing a submission will take time, and if you have nothing really worth publishing available, that might not be time well spent. It's up to you.