We can compare and contrast with Metal Gear for example, which had has similar release patterns.
The core gameplay of stealth and survival was the focus of Metal Gear Solid alongside some small forced-action sequences that served to quicken the pace, and some puzzle based boss battles. Metal Gear Solid 4 and Ground Zeroes still feature all of these with the exception of the puzzle part of the boss battles. Obviously I'm not suggesting that every sequel should follow the original mechanics perfectly, and as I say Resident Evil 4 and Metal Gear Revengeance were both great games standalone that completely changed the mechanics, but neither were great games in their series. I think it's healthy for long running series to try something different like those two examples as a sort of spin-off but then integrating them as a replacement for the previously successful mechanics seems a bit like you're not making a sequel but rather a game that is familiar to it.
In terms of characters, you have the main protagonists of Solid Snake and Chris Redfield that can be compared in how they are written.
Solid Snake is a genetic machine essentially built for destruction, death and war. Throughout the series he attempts to fight against his true nature but ironically he does so in the only way he knows how - by producing death, destruction and war. Numerous times he is doing what he believes to be correct and for the greater good only to find out later that his efforts were part of a larger plan that he could not see due to the information controlled that was given to him. He is still a machine of war and cannot break his cycle. Snake is an argument over the role of genetics in our destiny and if we can ever really escape them or will always be bound by them. He's an avatar to ask the questions about the morality of war and how a soldier doing the right thing at the time doesn't always mean doing the right thing, and whether we can ever truly blame people for following their morality in hindsight.
Chris Redfield is special forces soldier. He was rebellious in his time in the service which led to him leaving because The Man couldn't see the genius in him, and he moved into the anti-terrorism unit. He tried to retain some sort of normality through his relationship with his sister and seemingly taught her how to be a top level special forces operator in his spare time. He tried to take down Umbrella but couldn't because corporations bribed people. Let me restate this, he tried to tell his superiors that a corporation in their city had built and were using a doomsday device that would result in an extinction level event but they didn't care because they had been bribed. How much money did these people receive? How did they plan on spending it? After about 4 games he killed Umbrella and joined a new anti-terrorism type unit. Chris is a soldier. He has a sister that he really cares about. That's literally all I have.
Chris is a good example of the problem with the Resident Evil games. He has appeared in about 5 of their games, and been a plot point in others where people are searching for him, and I know almost nothing more about him than I did after Resi 2. I have no idea why he does things that he does that don't involve his sister apart from the fact that the plot tells him to do it. After Raccoon City, why did he decide to run away and investigate Umbrella? What were his investigation skills like as a man who spent his entire time being trained to shoot people?
The people in Resi just seem to exist in the manner of a Hollywood action hero which is a pretty apt comparison as they are starring recently (with the noted exception that you made about Revelations), in action games and action films. This is somewhat disappointing as the original plot in Resi 1 and 2 was actually well written and engaging. You had a feeling that everything that you were doing mattered in the world and mattered to the character. Resi Nemesis wasn't as well written in terms of characters but thematically it changed these bad ass superhero soldiers into vulnerable people who were hunted by a monster that they couldn't just kill by sheer force (until of course they killed it at the end using sheer force) and it brought another layer of depth to them.
I think a good way of explaining it is that since Resi Nemesis, the series has just become lazy in terms of setting up their plot and making their mechanics inform gameplay to the point of where now it just doesn't make much sense. Here's the character you're playing, here's the Villain of the Week, here's a range of weapons and see you later. Any questions you have can be answered with "because Umbrella". Cheers for the £50, byeeeee.
Considering how good the series was in its former glory especially the sophistication for its time, its just disappointing to see it become more and more hollow as time goes on.
