They are undergunned, obsolete and out-classed by every other frigate on the planet (including ours) but other than that, they're nice little ships.
The Royal Navy, along with only the French Navy, is a Rank 2 Blue Water Navy with power projection capabilities. However, the RN will maintain its position as Rank 2 in the coming decades whereas the French Navy is likely to lose that position.
The Royal Canadian Navy is a Rank 5 Non-Blue Water Navy, along with Saudi Arabia, Norway and Israel, limited only to coastal defence within and slightly beyond the EEZ.
Let's also compare the Royal Navy's Duke-class frigates to the Royal Canadian Navy's Halifax-class frigates:
Duke-class
Anti-air missiles:
1 × 32-cell Sea Wolf GWS.26 VLS canisters for 32:
Sea Wolf (range 1–10 km) or Sea Ceptor missiles (1-25+ km)
Anti-ship missiles:
2 × quad Harpoon launchers
Anti-submarine torpedoes:
2 × twin 12.75 in (324 mm) Sting Ray torpedo tubes
Guns:
1 × BAE 4.5 inch Mk 8 naval gun
2 × 30 mm DS30M Mk2 guns, or, 2 × 30 mm DS30B guns
2 × Miniguns
4 × General-purpose machine guns
Aircraft carried:
1 × AgustaWestland Merlin HM.2, multi role helicopter, of 829 Naval Air Squadron, RNAS Culdrose, armed with;
4 × Sting Ray torpedo
4 × Depth Charges
2 × General-purpose machine gun
1 × M3M machine gun
or
1 × Lynx HMA8, armed with;
4 × Sea Skua anti-ship missiles, or
2 × anti-submarine torpedoes
Halifax-class
24 × Honeywell Mk 46 torpedoes
16 × Evolved Sea-Sparrow SAM
8 × RGM-84 Harpoon SSM
1 × 57 mm Bofors Mk2 gun
1 × 20 mm Vulcan Phalanx CIWS
6 × .50 caliber machine guns
Aircraft carried:
1 × CH-124 Sea King