Is this a good opening?

Is this a good openning? or is it useless?

The problems with 4.Ng5 are

i) Moves a piece more than ONCE in the opening with no tactical reason to do so, which is a violation of the most basic principles of the opening.   You just don't make cheapo attacks right out of the opening "hoping" your opponent won't see them. White is better suited to developing his other minor pieces, castling or anything else that helps development harmoniously.

ii) As indicated in i),  the threat on f7 is easily dealt with Qxg5 at which point White is down a piece, should consider resigning.

I believe the 4.Ng5 line is useless.

It is good for white. He gets 6 points lead in material.

The problem is, that this opening is unlikely to occur at games beyond beginner level After 4. Ng5?, Black could have played 4... Qxg5 instead of 4... h6?. He could have also played 5. Qf6, threatening 6. Qxf2#. So, it is unlikely that exactly this position will occur, because there are many mistakes, blunders or inaccuracies in this opening.

There are openings, for example Fried Liver Attack, Lolli Attack and Traxler Counter Attack, that use similar ideas.

Simply play 4...Qxg5.

In case you had played 3...Nf4, you play now 4...Bc5. The initiative belongs to who has more active pieces, so you develop another piece, ignoring your opponent's threat and creating your own threat against f2. Be prepared for blood.

thanks!

If you're opponent don't see it then it's a good opening

4... Qxg5 5. d4 Qxg2 6. Rf1 Bxd4 and white is 2 more points down in material:

No it is a terrible opening

It's not terrible, it's unlikely

I wouldn't mind playing white after this opening. But my opponent would, so he wouldn't let it occur