When and if you elect to return to OpenBSD:
- To my knowledge there are no plans to be able to mount ext4 filesystems. You can mount ext2 or ext3, as the latter is ext2 plus journaling.
- NTFS filesystems can be mounted read/only. Fuse support has been added to OpenBSD (for 5.5), and there is a working ntfs-3g port for read/write mounting -- it works for me -- which will likely be a binary package for 5.5.
It's too late to diagnose your NTFS filesystem problem, as you're no longer running OpenBSD, but with the limited information provided I assume one of these are the likely root cause of your failure to mount:
- The drive had an OpenBSD disklabel installed that was misconfigured.
- The drive did not have an MBR installed. OpenBSD requires either an MBR or a disklabel.
- Correct MBR/disklabel but the NTFS partition was not in clean state (e.g.: Windows "hibernated" or otherwise not shut down)
- Typographic error in your mount command.