Pros
I've learned a lot about problem-solving and working with a ton of different tech stacks while working at Capital One. My experience growing from mid-level to senior engineer here was pretty positive. Overall the company pushes towards modernization and cloud-native solutions, so you're likely to spend time working in both new and old tech, but will be bridging the gap between them and ultimately migrating systems to newer technology, which you'll then build new features upon. I definitely encourage folks to move around teams during their time at Capital One, so that you get exposed to a broader variety of tech. The engineering division is huge and internal mobility is very easy - usually you can move after just 6 months in your role as long as you're in good standing. You're likely to find a team you'll enjoy working with if you look around. And if you join out of college through their TDP program (which I did not, but know many who have), you'll be expected to try out 2 teams over 2 years, so it's a great way to get started in the industry.
Cons
The biggest downside of Capital One in my experience is the performance management, which still uses stack-ranking to pit employees' performance against each other to decide who stays and who goes. For years, I thought "no problem, I'm good at my job, I'll never be in the bottom 10-20%". And so far I have not been. But I've started to see very talented people who I respect fall into this bucket. Senior engineers (and above) who spent more time advocating for and building solid, reliable, maintainable software have been put on "coaching plans" because they're not pushing for the newest, half-working flashy feature that the higher ups want. They ultimately end up leaving when this happens. I've built my career on creating solid foundations in software, with hard evidence to back the claims that these foundations work, and the evidence I bring has started to get repeatedly ignored by senior leadership, while they push unfounded, last-minute changes on us from the top. I fear that I may ultimately fall into the same performance management trap. That said, your experience as an engineer here is highly dependent upon your team, your manager, and senior leadership. I've had teams which have given me some flexibility to work on projects I consider important, but other teams which actively discourage it in favor of prioritizing whatever senior leadership asks for. And I find that it's only a matter of time before any given software engineering team falls victim to this top-down management push, once some group of leadership gets shuffled in who "has something to prove". The bright side is that it's pretty easy to move to another team internally. Make connections while you're here and follow the good engineers (and good leaders) to their organizations, and you'll do well.