For me this can only be Minna de Spelunker or Spelunker HD. This is because it encapulates what it means to be a gamer.
At it's core Spelunker HD looks simple, but is anything but simple. You see every level was expertly crafted to not just offer gamers a challenge, but to also play tricks on your mind. For instance the geyser trap was pretty common, though you might find a level with none of them. Naturally you will start feeling cocky and ultimately end up jumping into one. Another masterful trap is far later on when you think the geyser is going to go off, but actually spikes will pop out of the floor killing you for not progressing faster. Think Spelunker is a one trick pony? Well you're wrong because there were also several traps that only LOOKED like they would kill you. Since you assume their presence means death, you're actually making several parts harder than they actually are. This is the type of design you just don't see in games anymore and thats a real shame.
Speaking of things we don't see anymore, Spelunker also added themes for each area. This means there will always be a new element to master. Whats truely amazing isn't that there are themes, but any true Spelunker never forgets those themes. No one goes into area 7 trying to remember what to expect, they always remember the bird from 67. This is true for all the area's and a testimate to how memorible the traps were.
If you're not impressed by the level design, thats fine because it also does the homage correctly. This gen we've seen several old series continue on. Megaman got 9 / 10, Sonic finally got a 4th chapter, but none of these titles surpass the originals. Megaman was on par with the originals and Sonic actually had less, but Spelunker has OH SO MUCH MORE. The original game had 5 pathetic levels, where as HD features a whopping 100. None of the original levels are reskined, but several elements / designs make an appaearence. Additionally the game goes one step further and blows away fan expectations.
When it comes to games trying to capture the past, fans are typically never happy. Sonic fans would rather have a 8bit / pixeled game, where as several Megaman fans would love to see the blue bomber in stunning HD. However Spelunker features the iconic NES look, which is so well done that you might not actually believe the game is mostly new. To support the NES look, the game also features sounds that will bring a smile to anyone from the cartage era. However if you're a new comer the game is also in glorious full HD.
If this isn't enough for you, there are two multiplayer modes. The first is a slightly different version of the single player campaign. This version has some minor changes to the level, in addition to several new elements. These include killing you if too many people get in a cart / boat, red ropes that break if 3 people get on them and finally yellow ropes that drops down if enough people get on it for a shortcut. The next is the ability to play with 6 people online or 4 people offline via splitscreen. Whatever mode you select, you will have the ability to use universally understandable icons so everyone is on the same page. The other mode is a simple race mode, though it is quite exciting if you have 2 spelunkers of equal skills.
The truely amazing thing isn't that Spelunker had all this content or anything, it was the amazing value. With all this content, home rewards, and a platinum trophy, who would believe it only cost $10 dollars?! Having played games for $60 with less content, it baffles the mind to think that this title would get overlooked by anyone.