There are plenty of interjections that can match, depending on the context.

Some will be close to the English “man”, being directed at a male interlocutor that you want to take as some sort of “witness” to your feeling of enthusiasm, surprise, disappointment, etc.:

1. mon gars (no equivalent for a female interlocutor)
   

   C’est bon ça, mon gars !

2. mon vieux (or ma vieille for a female interlocutor – even used with young people, means “my old friend”)
   

   Ben mon vieux, t’as pas de chance !

3. mec (sounds very much “teenager French”, originally used only for boys, but I have heard it recently used among teenagers even for talking to girls, even though there is an equivalent meuf)
   

   j’adore ça, mec !

4. mon ami(e) (sounds a bit old-fashioned, so rather used with a touch of irony or sarcasm)
   

   Mon ami, tu sais pas ce que tu rates !

We can also have, like in America :

4. bro (between brothers, for girl : “sista”)
   

   Ça va bro ?

I use it sometime with my bro in the L.ord.

As an interjection (as opposed to an apostrophe, which Gregorycrene covered), there are many terms which vary significantly between places, socio-cultural settings, etc.

Old-fashioned and/or local :

• Doucement, pardi ! (Man, slow down!)

• Mazette, tu en as mis du temps ! (Man, what took you so long?)

Neutral :

• Mince alors, c’est un super exemple ! (Man, that’s one good example!) (works with both good and bad denotation)

• Aïe, la voiture est encore en panne ! (Man, the car is broken again!) (only works with bad denotation)

• Eh ben, ça faisait un bail ! (Man, it’s been ages!)

Familiar, up-to-date :

• Sérieux, j’en peux plus ! (Oh man, I can’t take it anymore!)

• Mon gars, t’as vu les infos ce matin ? (Man, did you watch the news this morning?) (not an address but an interjection in its own right, just like Man)

Slang :
The M word comes to mind, as well as a couple others 🙂

About man in “Man, that’s good.“, I don’t think there’s a word to translate it, and depending on the context it might get lost in translation.

For two people in a jacuzzi, I’d say

Qu’est-ce qu’on est bien !

But if you’re tasting food or a drink, I’d say one of those

Hmm, c’est super bon !/C’est vraiment très bon !

or

Qu’est-ce que c’est bon !

which is even stronger. Qu’est-ce que can also intesify negative things like :

Qu’est-ce qu’il fait chaud ! (Man, it’s so hot!)

For something annoying you can use sérieux ? or sérieusement ?. Like in “Man, you forgot your keys again? It’s the third time this week!“, even in English you can use seriously or are you kidding me?.

And I can’t think of anything (yet) for something sad, like the “Oh man, I’m sorry.” when you hear a bad news. I’d think you’d just omit it.

From a Quebec perspective, the anglicism “Oh boy!” is quite common. Though such integral loans from English are heavily frowned upon by many, and chased down like vermin by language institutions in place in the province, this one is still alive and well in familiar speech in 2019.

• Oh boy que c’est bon ça !
• Oh boy ! Qu’est-ce qu’on va faire, maintenant ?

The fact boy is a masculine term is a bit blurred by the fact it is not a French word, but a basic knowledge of English has been common for centuries in Quebec’s population, so its masculinity is not a very big secret. However, this masculinity, though not secret, has also been masked away one layer deeper by the fact it has more or less become a set expression, like the “Man!” of the question. So there is no problem for one to say it to a woman, and women together without men around can still use it quite naturally and without any sense of ridicule.

Un peu comme en discute une autre réponse, Larousse en ligne a choisi le juron ou locution interjective populaire bon sang :

man, was it big! / bon sang, qu’est-ce que c’était grand !

C’est un choix et ça ne veut pas nécessairement dire qu’on choisirait man pour rendre bon sang, comme en témoignent Wiktionnaire et même Larousse en ligne lui-même.

With an Acadian dialect, you can say

Merde, couillon, C’est Bon!

Also, that does not mean what it does in France, as couillon means fool, or dude if used in a friendly tone.