Quote: "...free, easy to use (preferably something close to a point-and-click UI), MIDI sequencer for Windows?"
A pretty decent easy to use one is
Anvil Studio. It has a lot of options including entering notes via score. It also has a pretty decent drum machine. You can set up loops and such.
A pretty meaty one with lots of functions and controls is
Direct Music Producer
I'm not exactly sure why Direct Music as part of Direct X was deprecated, probably because it was combined into Direct Sound or something - but at any rate, I find this to be a very top notch piece of software in terms of what can be done with it. It's a bit difficult to get used to, because there are so many layers and options, but midi wise, you can pretty much do anything you want. And you can create a sample library wave table that can be triggered by midi. The format is called DLS (down-loadable sounds I think). This format never really caught on as it's own but SF2 - sound fonts - is based on this format. If you running windows os, there is likely a file called gm.dls. This is a midi wave table that is used with the Microsoft synthesizer. If you run 'dxdiag' and click on the Music tab, choose Microsoft Synthesizer and click on Test. You'll here the wave table in action.
You don't have to use DLS at all, but it's there if you want to build or use your own wave table libraries.
Check out
Synth Font.
This uses sound fonts to play midi files. It also has a midi editor. I used to use this years ago, and back then it was good so I can only imagine that it has improved.
Enjoy your day.