Yeah depending on how you define success, those two had the lion's share of third party titles from their respective generations, including some of the greatest games of recent years.

I'd also throw in the OG Xbox, as its sales were quite low and it lost a ton of money, but it had a ton of third party bangers like Star Wars Battlefront 1-2, Doom 3, Panzer Dragoon Orta, Ninja Gaiden Black, the Splinter Cell and Burnout games, Chronicles of Riddick, the Timesplitters games, Max Payne 1-2, etc.

Fun facts: The Gamecube and Xbox were neck-and-neck in sales, and the GameCube not only broke even, it turned a small profit where the Xbox lost millions for Microsoft.  If the Gamecube was a failure, the Xbox definitely was. 

Yeah I like the Xbox a lot, it's my favourite 6th gen console, but I don't really see it as a success due to its low sales and the massive amount of money it lost.

FM Towns Marty

PC Engine/TurbografX, Sega Saturn and GameCube for me, in that order. Dreamcast is just lurking outside and just doesn't make it due to being so cut short.

You could add the Sega Master System as it failed in the US and got beaten by the PC Engine in Japan, but in Europe and especially Brazil it was anything but a failure, and it's library shows. If it counts I would put it in front of the Saturn, thus pushing the GameCube out of the top 3.

Brand establishment.  NEC and Panasonic tried to establish gaming brands and couldn't, while MS did make xbox a recognizable brand.  Xbox also sold more than Sega's first console in the master system.  And for their first outing, to beat Nintendo in sales was note worthy.  

It isn't unusual to lose money in order to establish brand.  Amazon bled money for the 9 years, now look at Amazon.

Business is s bit more complicated than sales and initial profit.

I still reckon 360 could have succeeded without the OG Xbox, in much the same way NES and PS1 succeeded without an established bridgehead preceding them.

Xbox was a valiant first effort, but the way I see it, it was more a case of "if at first you don't succeed, try again." They learned from their first console and came back swinging much stronger with their second.

Oh, I greatly disagree with that.  The OG established Halo as a legit top tier franchise, also pulled in a lot of PC only type of games.  It set the stage for the xbox 360.

I work as a technical lead in general product goods, losing money is expected in the vast majority of cases.  It is hard to establish a brand, very rare to take on the big dogs (e.g. name brands) out of the gates.  New products typically have higher CoGs due to lack of volumes, Ops costs are high because efficiencies are a WIP, Capex is still being paid off, and profits are low because you have to sell at an aggressive price.  The purpose of the OG xbox was brand establishment and it was successful.

As for the NES, there is a reason 9/10 gamers will say it is the most impactful console in gaming, what it did cannot be considered the norm, but should be celebrated for the outlier it is.  As a rookie Jordan average 28 points on 52% shooting but expecting other rookies to do that is crazy.    

Sony, good for them for being ready to take advantage of an opportunity, but I do personally think they got luckier than they were skilled.  Sega via the CD, 32x, surprise launch of a super expensive Saturn..  lol, Sega committed suicide.  Nintendo arrogantly stuck with cartridge, which was expensive.  Make a N64 game with carts being $15 or make a ps1 game where CDs were $0.50?  Sega was dead and buried, Nintendo was too expensive, so everyone went Sony.  Again, Sony deserves credit for being prepared, but my lord did the big two just stupidly hand the market over to the Sony.

Google and Apple want into gaming, so did Amazon..  yet none were successful.  MS did establish xbox with the OG.  It was a successful console.    

The 360 had a lot more going for it than Halo though; Halo certainly helped, but also had other killer exclusives like Gears of War, Mass Effect, Bioshock, etc plus crucially it offered a more affordable and usually technically superior way to play almost all the big third party games like COD, at a time when the PS3 was prohibitively expensive and got mostly inferior ports.

It wouldn't have sold quite as much, but the 360 would still have done well without Halo, it wasn't a one trick pony.

the 360 was more Halo, but Halo established as a must own system seller.  I would argue stuff like Jade Empire/KOTOR/Morrowind set the stage for expectations for Mass Effect.  I will maintain, may have to agree to disagree, the OG made it clear this was a 3DO venture; MS was serious and worth considering as a main player.